If you only have relatively small areas of bare metal to etch you can always refer to the old cotton cloth or rag method of applying acid etch, you only need to wipe over the metal to create a key for subsequent coats.
An isolator is supposed to sit on top of previous layers without softening the paint surface underneath, Acid etch or etch primers are solvent baring paints that use aggressive solvents that will nearly always cause solvent reactions particularly on unknown paint finishes.
I have a tin of unused isolating etch primer in the garage but it's only suitable for use as an etch primer, I think the so called isolating properties mean "isolating bare metal" were there'd be no risk of solvent reaction.
Acid etch as you probably know is a resoluble solvent product whereas the traditional isolator or barrier coat is an alcohol non soluble form.
Is it possible to apply UPOL's Barcote isolator for example on freshly painted synthetic finishes without any adverse solvent reaction.
The two products are entirely different paint types with two completely different uses and IMO should not be confused.
Hope this make some sense?
Steve.