Pipetting strong acid with plastic material
This depends on type of plastic. You definitely can if plastic is perfluoropolyetylene (Teflon). You probably can if plastic is polyethylene or polypropylene, but both will degrade in long term (polypropylene will do it faster). You should not, if plastic is PET or other polyester, or polystyrene.

It is probably most reliable to find which plastic you dealing with and search for 'chemical resistance chart' for this plastic.