"adjust the power increase as circumstances require"
well.. there is a lever under your right foot...
you can always make or get a switchable evrymod.
I made a simple switch to work on a bmw tds (same ecu system as early tdis) the "rear electric windows lock" switch became a selector between stock chip and a preformance one, 90Hp/117Hp, is that kind of a system you were thinking?