I know that in sama Veda many mantras of rigveda and yajur veda are repeated so that must mean that language is similar throughout Vedas, but does the vedic Sanskrit change between rig, yajur and atharva Veda?
Even in the Rig Veda, 10th mandala language style is a bit different from other mandalas. It has younger linguistic features as it was written at the later ages. Atharva Veda language style also differs from Rigveda.
Ref. The Rigveda: The earliest religious poetry of India. Stephanie W. Jemison and Joel P. Brereton.