Variables can be logically arranged in groups (e.g., input, output, network etc.) such that most sub-actions just change one group, and usually all/most of it:
group1 == <<a,b,c>>
group2 == <<d,e,f>>
group3 == <<g,h,i>>
/\ a' = a+1 /\ b' = b-2 /\ UNCHANGED c
/\ UNCHANGED <<group2, group3>>
This way, adding a variable requires editing only those subactions that work on that group.