I cant help with that, i never worked with memory, but i see that the main thing to do is to stop that address to update this displayed ping (otherwise RSC must update it faster) and then you can give it a new value to show and if nothing else is changing it, then it will be freezed.
(in CheatEngine i used debugger to find out the adress, then there is an option "replace with code that does nothing", after that i closed debugger and the ping was freezed).
The real ping in server is actually changing as you know, so maybe the new value should have some +- range to float, i mean if the user has ping 20 and he changes it to 35 then its should change maybe between 33 to 37 after some random interval to look it more realistic, but if its too complicated dont waste time.