[Slice]

Lowering the client fps by purposely causing lag is just stupid. The only way I see you could enforce a limit on FPS would be to kick/punish players that has fps above x (reading the FPS by using JernejL's method) and tell them to go to display settings, turn "Frame Limiter" on then type /fpslimit x.

Note that the value you put in /fpslimit won't be exactly the FPS you get. (fpslimit 48 usually yield 45; 32 usually yield 34).