I disagree with suggesting you could look at just part of an object with a narrow field instrument and balance the colours in an arbitrary fashion at that location, but in a wider field you would use a different histogram and that's all OK
Doing so distorts the intrinsic colour spectrum and amount of flux/light emitted from parts of the object.
It may make for a pretty picture, which is fine, but tells us nothing about the relative physical processes going on. The fact we arbitrarily assign SHO colours is license enough...but locally vary the intensity? Nup.
I was at Wangi Falls in NT a few years back...and took some snaps of the falls. There was too much green, so I re-balanced the histogram....
As I said, no law against it.