I found a way to use Ply's Mod for what you sorta want to do. My test code is as follows:
;Artificial Intelligence Script
;Header
desc = increase velocity of player?
;Triggers
:state=0,plrwithinzone=1:state=1
:state=1,scancodekeypressed=33:state=5
:state=5:syncrate=100,state=10
:state=10,scancodekeypressed=54:syncrate=40,state=0
;End of Script
This is just test code and it can easily be modified.
I simply set up an area of ground segment. Place a player marker on one end of it and in front of the player a trigger zone.
State=0 - waits for player to enter zone and changes state to 1
state=1 - waits for user to press the "F" key, Once pressed changes state to 5
state=5 - sets the syncrate to 100 and state to 10
state=10 - waits for user to press the RIGHT-SHIFT key, once pressed changes syncrate to 40 and changes state back to 0
Player has to reenter zone to be able to use these keys again. Also a timer can be used to reset the syncrate.
This would require Plystire's mod. If you should decide to try it, be sure to copy the original FPSC-Game.exe and even change the name of it so you have two copies before placing Ply's mod into the FPSC folder. It's as simple as that. If you don't like it then rename his mod (FPSC-Game-plystire.exe) and copy the original exe file into the FPSC folder.
Because of the scripting design and a bare minimum of commands, you cannot hold down a key to do an action. The has to be pressed and released. Also, the assigned value of the key pressed is stored and a key cannot be easily re-used so if you want a reverse action you need to select another key to do this. Also, certain keys have their own use to the engine such as "w,a,s,d,c,r,space" and etc. So you have to be careful making key assigments. So "r" for run would not work as that would force the player to reload.