Freezing fat is a procedures to get rid of fat cells after they die in freezing, I do see it as a medical procedure for the wellness of the person, so yes it should be fine.

 

Changing skin color is also permissible as it naturally happens with more sun exposure or less. The conditions that I need to remind you about are:

 

1- Not to cause harm to the body.

2- Not to base it on the intention as rejecting what God gave you. Just for beautification is fine.

 

Allah Almighty knows best.