Prexe Variables

From Manual :

$RGSPD_PREXE

Register Speed Pre Execution

This variable controls the interpreter pre-execution when a register value is used for the speed parameter. The default value is FALSE which means to stop the pre-execution. If it is set to TRUE, the pre-planning is not stopped. In this case, if the user changes the register used for the speed immediately before executing the motion, the speed used will be the previous value of the register. If the register is not typically changed right before issuing the motion then it may be safe to allow the pre-execution to occur.

Power Up : On_Cold_Start

NOT From Manual :

My interpretation would be that if these variables are set to true, your program will read the values of registers used as indirect values well before their actual execution, and if they are changed after that reading, the change will not take effect in locations where they are used as indirect values, such as the speed of a move. When set to false, the values will be read at the line they occur, allowing on the fly changes right before their use.