Changing to a different plug, one that is also designated for the same use? Why on earth would anyone have an issue with that?
Or, for that matter, any other type of connection? There's no requirement to use a NEMA pattern plug.
"Altering" the product? Might as well just leave it in the box. Can't be too safe!
We can carry this 'listing and labeling' silliness too far. I recall one time when someone got all upset when a 'flammables' cabinet was painted to match the other cabinets and equipment in a workshop. "They HAVE to be yellow," it was asserted- despite being shown catalogs with such cabinets in yellow, red, orange, white, black, and grey, as well as brushed stainless. Made me want to paint the thing pink, with purple polka-dots, just to stir the pot!
Likewise, we've had discussions here as to whether it's allowed to actually use the new CFL and LED bulbs- after all, the fixtures were never evaluated for use with them.
Makes me wonder if it's OK to play porn films in my DVD player ... I mean, did UL 'evaluate' the player for use with porno films?