Substitution after made free throws

[vawils]

I have asked a similar question before but still request some feedback to get this straight. After a made final free throw I know they can sub for the shooter etc. How about annoying coaches who sub after the first of two shots and then decide at the last second to send in a couple more subs to the table as the guy is shooting the second shot? Is it ok to let them in after the made free throw? This could apply to subs for either team. I assume so, but why then do we try to get them in after the first of two shots in the first place? Some coaches are always trying to push the envelope of course etc. I am still confused a bit about this and still learning so appreciate feedback so I can get this right for sure. Thanks a lot.