Is it a problem of koveish yerakot to prepare a large batch of coleslaw Friday night, some of which is for immediate use and some of which will sit with the dressing (including lemon juice and vinegar) until lunch which improves its flavor?
Shulchan Arukh OC 321:3 says that pickling is forbidden on Shabbat because it is like cooking, although not Biblically, obviously, because it doesn’t use fire.
In this case, if one were to eat it all at once, nothing would be pickled, but if one waits until the morning the dressing has the effect of pickling.
If that was not one’s intent – they’d be happy to have it taste the same in the morning, but the reality is that it will be better in the morning – I think it is mutar without a doubt. First, it can be framed as a pesik reisha denicha leih in an issur derabanan, which some argue is permitted (and some disagree).
More to the point – the focus here is on the act – כובש כבשים דנראה כמבשל – not on producing something pickled. Since the act was done fundamentally to create a dressing, it is not an act of כובש כבשים.
If one is doing it specifically with the intent that it be pickled in the morning (unlikely) – then I think one could still argue that this act is not seen as an act of pickling, since to the normal onlooker you are not doing an act of pickling, but of making a dressing. So unless it is commonly done to make a lot for the sake of pickling, I don’t see here a problem at all, even if one has this in mind.