Verse 9.23
Krishna says that he who worships other gods worships him (i.e. Krishna), now why does he say so? because he (mahavishnu) is the supreme godhead and all the other gods are his ansh(part) or have been originated or created by him.
So if they worship him by making him look like any different god it is okay they will be blessed because they are ultimately worshipping Krishna the supreme being.
Verse 9.25
It states that when a person worships a demigod he will be born with that demigod or whatever he is worshipping. Now consider for example that a person worships kal-bhairava (in some forms bhairava requires alcohol and meat as offerings) so if you worship demi-gods with such qualities you will tend to posses such qualities which in turn affects your karma because you are not going towards reality i.e. away from material pleasures which is where ultimate truth lies.So worshipping demigods is not wrong but just sticking to a demigod and considering it bramhan even though we all know the reality that Krishna is supreme, it is totally foolish and sensless. What's more foolish is that you are just taking material aspects(like meat eating, smoking weed, drinking,sex etc) of worships of demigods rather than seeing the qualities or making them tool for reaching the ultimate goal.
Supreme Bramhan in its pure form is Krishna if you worship him you will attain liberation i.e. you will live with him.