I customize the list all the time. It’s very easy. I have a standard assortment of materials that I carry (20 Artemisia, 20 Mushroom, 20 Human Bones, 20 of the lowest Poise/Stamina/Focus potions, etc). Basically junk, plus whatever blue items etc I pick up during the run.
Just start by adding 2 of say herbs, if it’s an affix you wanna keep, add another 2 of that same type. When you get a corruption from your no-no list, you subtract the last 2 you donated. It will remove that corruption. Then move on to the next material. Rinse and repeat.
If you add a certain amount of a material all at once, it can/will change the affixes you would have gotten from adding them incrementally. So if you get an affix that keeps popping up, add 8-14 of something (even the item you were just trying); you will get 3-4 affixes all at once which can often not include that one you were trying to avoid.
Once you have 10 corruptions, commit the offering. The Plague won’t be at max yet, but it will lock in the corruptions so they will not be changed with further donations. If you do it all in the same session, the new/extra stuff can change the current corruptions.
After the commit, then add whatever items you want… gear, embers, more mats, whatever… to max the plague and commit. Now you’re all set with affixes you are OK with that doesn’t hurt you much.
And while I made a point to articulate the steps verbosely, once you know how it works it’s a pretty quick process.
PS. The affix is based on the item that caused the actual affix to appear. So 1 Potatoes + 1 Herb, will give the same affix as 2 Herbs.