Normally I wouldn't want to edit the active tool offset as there are parameters as to when the new value actually takes effect. I would consider changing the stored value of the offset used for the tool prior to activating it.
The variable number to set tool compensation depends on what type of offsets you have.
#10001 = tool offset 1 for tool comp a
#11001 = tool offset 1 for tool comp b and geometry height for tool comp c
#10001 = tool offset 1 wear height comp for tool comp c.
You can use #2000 series if less than 200 offsets.