FPS unlockers don’t alter any files nor have a reason to be disallowed.
It was mentioned at RDC once that fps unlockers are perfectly allowed.
Hopefully soon enough we’ll get support for this FPS cap to be lifted and no longer need to use external programs, as for the error, I’m unsure however I would just ignore it, doesn’t seem like anything significant other than showcasing what change it made for the higher FPS.
Like @wickedyboo explained, FPS unlockers aren’t against the rules
as for the “error message” you’re getting, you’re using the latest version of rbxfpsunlocker. However due to Byfron, memory management has been locked down a lot more.
rbxfpsunlocker gets around this by setting the target FPS in a JSON config file, shown in the path. So, you need to relaunch roblox for it to take effect.
But you said “roblox can be very laggy,” your fps unlocker will not fix the lag, what it does do is “uncap” your fps from 60. Which means that unless you are hitting 60 frames per second normally, you won’t see any improvement.
try to close everything, then start the fps unlocker, then start roblox and check your fps
(edit: just to explain a bit more the message you were getting wasnt an error message, it just notifies you that its changing the config file and you need to relaunch roblox)
FPS Unlockers are not against the rules ; however, modifying the client’s process space is, and we have no way to distinguish between malicious software and FPS unlockers, as they do essentially the same thing. The link above gives some further information on the topic and also explains how to unlock FPS the legal way.