This Part of the Manubhashya of the Manusmriti says that if a Well-Behaved Hindu Kshatriya King takes over a place which was originally Mleccha Desh and people of the Four Varnas start living there then it wouldnt be Mleccha Desh anymore

Manubhashya of Manusmriti 2.23

When again it is said that ‘beyond this is the land the mlecchas,’ this also is purely descriptive of the usual state of things; the sense being that in these other lands it is mostly mlecchas that are born; it does not mean that people inhabiting them are all (on that account) ‘mlecchas’; because what is a ‘mleccha’ is well known, just like the ‘Brāhmaṇa’ and other well known castes. In fact, the name ‘mlecchadeśa’ is to be taken literally, in the sense that it is ‘the country of mlecchas’; so that if mlecchas happen to conquer a part of Āryāvarta itself and take their habitation there, that also would become ‘mlecchadeśa.’ Similarly if a certain well-behaved king of the Kṣatriya-caste should happen to defeat the mlecchas and make that land inhabited by people of the four castes, relegating the indigenous, mlecchas to the category of ‘Chāṇḍāla,’ as they are in Āryāvarta, then that which was a ‘country of the mlecchas’ would become a ‘land fit for sacrifices.’ And this for the simple reason that no laud is by itself defective; it is only by association that it becomes defective, just as it is when soiled by impure things. Hence, even apart from the countries designated here as ‘fit for sacrifices,’ if, in a certain place, all the necessary conditions are available, one should perform his sacrifices, even though it be a place where the spotted deer does not roam. From all this it follows that the statement—‘this should, be known as the country fit for sacrifices, and beyond is the land of the mlecchas’ is purely descriptive, being meant to be supplementary to the injunction that follows in the next verse.—(23).

Would Dwijas be allowed to move to Hindu Majority Countries like Guyana, Mauritius, etc or Hindu Majority Places in Non-Hindu Countries like Leicester in UK, Edison in USA, etc outside of Aryavart and Bharatvarsh and still be Valid Dwijas?

Also I think these Verses in the Manusmriti and it’s Commentary are allowing even Dwijas to go to Mleccha Desh if it’s for Business

Manusmriti 9.74

A man having business may go abroad, after having provided for the maintenance of his wife; for a wife, even though virtuous, may become corrupt, when distressed by want of subsistence.—(74)

Manubhashya 9.76

It has been said that a man may go abroad ‘on business’; the present verse proceeds to show the several kinds of ‘business,’—the time of waiting varying with the nature of the business. The text has said nothing as to what the wife should do after having waited for the eight years. And on this point, some people on the strength of Context, say that she should maintain herself by unobjectionable industries.

Would this be Correct or No? Would Dwijas who leave for Business and come back still also be Valid Dwijas?

This Part of the Manubhashya of the Manusmriti says that if a Well-Behaved Hindu Kshatriya King takes over a place which was originally Mleccha Desh and people of the Four Varnas start living there then it wouldnt be Mleccha Desh anymore

Manubhashya of Manusmriti 2.23

When again it is said that ‘beyond this is the land the mlecchas,’ this also is purely descriptive of the usual state of things; the sense being that in these other lands it is mostly mlecchas that are born; it does not mean that people inhabiting them are all (on that account) ‘mlecchas’; because what is a ‘mleccha’ is well known, just like the ‘Brāhmaṇa’ and other well known castes. In fact, the name ‘mlecchadeśa’ is to be taken literally, in the sense that it is ‘the country of mlecchas’; so that if mlecchas happen to conquer a part of Āryāvarta itself and take their habitation there, that also would become ‘mlecchadeśa.’ Similarly if a certain well-behaved king of the Kṣatriya-caste should happen to defeat the mlecchas and make that land inhabited by people of the four castes, relegating the indigenous, mlecchas to the category of ‘Chāṇḍāla,’ as they are in Āryāvarta, then that which was a ‘country of the mlecchas’ would become a ‘land fit for sacrifices.’ And this for the simple reason that no laud is by itself defective; it is only by association that it becomes defective, just as it is when soiled by impure things. Hence, even apart from the countries designated here as ‘fit for sacrifices,’ if, in a certain place, all the necessary conditions are available, one should perform his sacrifices, even though it be a place where the spotted deer does not roam. From all this it follows that the statement—‘this should, be known as the country fit for sacrifices, and beyond is the land of the mlecchas’ is purely descriptive, being meant to be supplementary to the injunction that follows in the next verse.—(23).

Would Dwijas be allowed to move to Hindu Majority Countries like Guyana, Mauritius, etc or Hindu Majority Places in Non-Hindu Countries like Leicester in UK, Edison in USA, etc outside of Aryavart and Bharatvarsh and still be Valid Dwijas? Would this also mean that Mandirs and doing Puja in these places are also Valid too?

Also I think these Verses in the Manusmriti and it’s Commentary are allowing even Dwijas to go to Mleccha Desh if it’s for Business

Manusmriti 9.74

A man having business may go abroad, after having provided for the maintenance of his wife; for a wife, even though virtuous, may become corrupt, when distressed by want of subsistence.—(74)

Manubhashya 9.76

It has been said that a man may go abroad ‘on business’; the present verse proceeds to show the several kinds of ‘business,’—the time of waiting varying with the nature of the business. The text has said nothing as to what the wife should do after having waited for the eight years. And on this point, some people on the strength of Context, say that she should maintain herself by unobjectionable industries.

Would this be Correct or No? Would Dwijas who leave for Business and come back still also be Valid Dwijas?