I have a little information on this. My Mitchell repair CD shows that there was a modification to the Rex-Regina control modules for the '89 - 92 model 740/940. The purpose was to improve cold starts when low-volatility fuels were sold in the summer and to correct for idle dip when the AC came on. The mods brought the systems up to late '92 specs.

However, the change involved replacing the entire MFI (Regina) control module and sometimes the Rex ignition module. These two modules had to be compatable and there were several possible combinations which would work. The change also involved some re-wiring in the MFI connector.

Reference TP 31903/1

I could not find any reference to re-programming the PROM. In fact it would have to be an EPROM and most references I've seen on those involve sending the EPROM somewhere to have it re-programmed or replacing the EPROM with a new one. In the '95 Volvo data there was reference to replacing the EPROM in the LH 2.4 system to correct for poor cold starting. The tools referenced were the standard anti-static tools used in working with sensitive electronic components. These basically serve to bleed off static charges though conductive work surface pads and the handles of hand tools. There is also a tool used to extract the EPROM from its socket. None of these tools is a re-programming tool. Sorry I couldn't find any more on this.