Hello!
I've been quite successful in developing a personal ruleset for notion, at least I managed to achieve all articulation changes I needed. Notion has a sheer advantage of Sibelius in handling its ruleset, because it can store a ruleset per document, or even have a set of documents share a single ruleset and be uploaded with it.
All you need to do is create a folder called Rules in the same folder with your document (or documents). Notion will reference this file before referencing its default files. One of the first things declared in the ruleset is to which VST it should apply, so it won't mess with other rulesets that may be in place. For instance, as I still don't own all VSL instruments that I would like, I use Miroslav as a replacement, with the rules being VST dedicated, I can fiddle with my VSL rules as much as I want without messing the rules for Miroslav, which, by the way, are quite decent from default. This dedicated ajdustment is not possible with Sibelius dictionary. For instance I can say that if Miroslav is the VST it should play sforzandos by increasing the velocity by 10, but if the VST is VSL it should look for the sforzando patch instead, in Sibelius is either one or the other.
Making my VSL presets consistently I also managed to have a good response from Notion for all instruments I have, so, it doesn't matter which VSL instrument I load, the rules are applied equally, so the articulations work. It should work with all instruments, but I cannot do anything more advanced as I don't own very much from VSL, only brass libraries. I'm afraid the complexity would rise if the ruleset had to deal with percussion.
Notion website has a set of videos explaining custom rules, I followed it and managed to build my own, articulation by articulation, copying and pasting the instructions from the provided pdf. I don't think I should share the ruleset, as it's very specific and quirky, I think you would be better off building your own or actually improving from the VSL SE ruleset, which already handles percussion. Still, I plan to improve my own ruleset after I actually BUY Notion, all this experimentation I was doing happened while I was demoing it, and sadly the demo expired!
About handling heavy loads, I found that Notion is a crashfest when handling Vienna Instruments instances. At first, when I was doing simple tests with few articulations, I decided to use VI directly because it's simpler, each staff is linked to an instance. With my VSL brass section in place (10 staffs), Notion would crash everytime I attempted to change anything in VI. Using Vienna Ensemble through VST instruments, which creates a new staff which you have to manually create other staffs for each channel, this problem went away, using VE I did not have a single crash. Miroslav on the other hand, would also crash when I had 15 or more instances, but I assume this problem would go away if I had VE PRO and I could load Miroslav in it. The computer I was using is an i5 with 16gb RAM, which is not stellar but should fare better than that.
The problem is, I was away for a week and didn't work on my Notion projects again before the demo expired and I didn't manage to test a score that was, besides heavy in the VST department, also several pages long. I believe the problems would reappear.
