I was going to say that such thing was implemented, and now I realize that you talk about the pre-windows 7 version.
I wasn't sure when that window was implemented, I thought it was in 1.10, but maybe it was there aready with 1.8.6
Previous to 1.12, the window is very simple and was intended for a couple of scenarios.
Your scenario is supported and it is enough to write on the upper "mac" box the generator number to change, and in the lower mac box the machine number that you want it to have after the replace.
The pattern is not repainted until you close the search/replace window (and i'm not even sure if that was done before).
Maybe in 1.8.6 you were required to fill both, ins and mac. In that case, try to put FF in the ins box.
<[JAZ]> Pa pi pa pa pa pi pa.... ;ĚD