Science Buddies: "Ask an Expert"

This isn't really a science project more of something I was curious about.
Theoretically, if you had a human fetus or that of one mammal could you manipulate gene regulation so you could make it resemble that of a different mammal?

Theoretically, yes, but that's if you have different genetic codes from different mammals present during gene expression.

Honestly, it's obviously extremely risky if anything goes slightly wrong, but it would be interesting.