Substitutions part III

[Clark Kent]

As discussing Rule 3-3 (Substitutions) a question has come up. I've posted a few other questions in other posts (Subs part II) but have another one that I'd like your help with. I've searched the rule book but there may not be a rule and therefore an answer to my difficulty to figure it all out.

There is a rule that prevents a player to "re-enter" the game prior to the clock "properly" starting (3-3-4) but is there a rule that prevents a sub who comes in during the game to exit again prior to the clock "properly" starting.

For example:
Technical foul on team B. Team A's coach sends A6 in for A1 to shoot the technical FTs. After A6 shoots the FTs, A7 is then sent in for A6. Is that possible? And if so is there a rule or a "lack of a rule" to support that?

Thanks