According to wikipedia there exists a lot of ways to modify a protein (post-translationally). Just to mention few: phosphorylation, dephosphorylation, glycosylation... While phosphorylation requires an ATP molecule, the reverse reaction, dephosphorylation, does not.
How about the other process?
Do all modification respect this scheme (i.e. one transformation consumes ATP but the reverse transformation does not)?
If not, I am particularly interested to know if one transformation and its reverse transformation both requires ATP.