What is the difference between partial surrender of bonus from a policy and partial surrender of a policy?

It depends on what do you mean by partial surrender of bonus.

Any partial surrender will affect the projected final maturity.

Partial surrender of Reversionary bonus Affects terminal bonus and total projected amount, because you forgo your terminal bonus.

Partial surrender of Policy sum assured affects the total projected amount, but you get to keep the terminal bonus (which is based off the Reversionary bonus). So this is slightly better.

Read carefully what you are surrendering.

A partial surrender of bonus from a policy will not affect your main policy, but a partial surrender of your policy will affect projected returns or even maturity value!