Right now, I think there are no restrictions for derated TO after deicing. But down in 1989 McDonnell Douglas Flight Operations Test Support stated that:
" When OAT is at or below 6ºC and fluids have been applied, the use of derated thrust is recomended only when the assumed temperature and associated take off speeds are determined based on an Equivalent Weight which is 5% above actual takeoff weight.
When OAT is above 6ºC, standard derated thrust procedures can be used if desired"
Few months later they promulgated new and more restrictive recomendations.
I guess that, as far as deicing fluids have improved since then, nowadays they slide more easily off the surfaces.