Reports from the time of the match probably named the experts who might have supported Kasparov, and it's been the usual practice for the players to hold "consultations" with advisors during breaks, if the player wants to ask them for advice.

Some articles at the time suggested that Kasparov was given significant information about the program before the match started, but I don't recall specific info on how much information might have been released.

So far as I know, there's no rule - or tradition - permitting exchanges between the opponents once the match starts, in most matches.

For a match of this kind, the opponents are often permitted to demand "special conditions" that are sometimes bizarre, so it would be necessary to review the whole history of the arrangements to know whether "comments from the opposition" were expected or prohibited. It's the rules stated and recorded before the match starts that govern until the match is over, and I don't have much information on that.

John