Removing the # to activate the instruction again might be described as "uncommenting" the line.
If it had been described as "uncommented" or "uncommenting" I would not have had trouble understanding in which direction it was said. As it is described in the comments of the file it is confusing for me, this is why I asked, with the hope that the people here mastering English subtleties would tell me how to understand it presently. So I got the answer with the last explanation by TerryN. Thanks to both of you !
In fact I want to use prelink only for a few programs, and I don't want it to redo the prelink (which makes the prelink.cache file increase from 8kb to almost 500kb, then the programs I aim to get faster loaded are not loaded fast anymore). I prefer to do it manually if and when needed. Therefore I put the cron script in cron.yearly, and changed the number of days to 365.
Maybe just removing the executable bit to the prelink cron script would just do it... didn't think more about it yet.