Prior to First Contact and Scorpion, Assimilation seemed to be more of a surgical procedure during which the collective removed biological parts and added technology.
In Best of Both Worlds, Picard was rendered unconscious on the Enterprise and taken to the Borg cube where he was assimilated. Beginning in First Contact, assimilation starts when the Borg inject their victim with nanites via assimilation tubules and, prior to that film, no mention of that technology (the tubules) had been made. The nanites begin by attacking the blood cells of the victim and "grow" implants, presumably, using the minerals already present in their body
It bears mentioning that one of the methods the crew of the Enterprise considered in combatting the Borg in BOBW, was nanites. That doesn't mean the Borg were using nanites at the time only that a nanite attack could disrupt whatever technology they were using.
Alternately, the Borg COULD have been using nanites at the time of BOBW. In Scorpion, while preparing for the confrontation with the Borg, Voyager's EMH shows that he (and possibly Starfleet Medical) has knowledge of this technology. That knowledge, however, could have come from Hugh in I, Borg or from the Borg encountered in Descent or from the former Borg Voyager encountered in Unity rather than from the encounter with the Borg in BOBW.
The skin pigmentation change to Picard in BOBW always struck me as the Borg were changing him to fit their mold. His skin tone was part of his "biological distinctiveness" and it was altered to match the collective.
In the Voyager episode Survival Instinct, it is revealed in a flashback that the Borg had assimilation tubules as early as 2368 (one year after Best of Both Worlds).
To answer your question, no. The evidence is that when the Borg were a TNG only threat, Borg nanotechnology wasn't mentioned or even (really) considered beyond a passing comment Dr. Crusher made about the removal of Picard's implants being a "a matter of microsurgery." It does appear that First Contact and Voyager wanted to retcon the technology into (most of) the previous encounters with the collective though.