Louis - I'm still not sure I understand what you want to be able to do, and although you say "we", I see no mention of a project. I agree with Dale that using multiple stickers to add multiple maintenance categories is not a good idea. However, it looks like maybe you're working with the Cape of Good Hope project and the list of categories you give (without a project name) are an interim level between a Cape of Good Hope maintenance category of that name and the parent Category:Maintenance Categories.
So, with that information, I think that there are two different questions here. One about Maintenance Category Hierarchy, and the other about how to easily add maintenance categories without using a project box.
Maintenance Category Hierarchy
I think that the category hierarchy of having the various "Category:xx Project Needs xx" each nested under "Category:Needs xx" should be reviewed by the Categorization Project. Most projects have all of their maintenance categories collected under one project category, which is under Category:Maintenance Categories (Cape of Good Hope is one). However, I can see the appeal of the Needs hierarchy - especially for projects that share research bases, such as Dutch Roots, Cape of Good Hope, and New Netherland Settlers projects -.but I think that the question of cross-project standardization needs to be addressed. WikiTree has a lot of projects, and from what I've seen, most have a unique set of maintenance categories. Magna Carta project, for example, has defined 8 needs= parameters that are fairly broad (see [this page]; details are given in the profile the category is added to. These broad maintenance categories serve the needs of the project, as I suspect the extremely narrow ones you list serve the needs of the projects that use them. WikiTree has been moving toward standardization for a while now & I can see where all projects would be required to have the same maintenance categories if this hierarchy were established (I'd adjust, but I wouldn't be particularly happy). Not sure what a good alternative would be? Maybe by location? Or maybe just add each project's Needs Marriage Record category on the other's (if the reason for Category:Needs Marriage Record is to group together categories containing people with similar research needs - not just that they all need a marriage record, but that the same set of research skills/specialty might be needed to find the marriage record for all of them.) Another thought: I don't think that people profiles should be added to the interim categories (between the project category/ies & Category:Maintenance Categories) - [Needs Marriage Record] has about 50. Is there a reason the people profiles are there instead of under the the appropriate project-level category?
Adding Multiple Maintenance Categories
Are you looking to add the same project maintenance categories to profiles that the project does not manage as you do using the |needs= variables with the project box for project-managed profiles? If so, I think you need to talk to Aleš about that. The Magna Carta Project had that problem last year and Aleš solved it for us with the {{Magna Carta Project}} sticker.
Others have noted that stickers are not intended to serve a functional purpose, that they are intended to highlight something interesting on the person's profile page. The project's sticker notes a Magna Carta connection and is placed by text explaining what that connection might be. So the sticker serves both to highlight and add a category - which is allowed for all stickers - we just have [a lot!] of extra coding that allows a project maintenance category to be generated using a |needs= variable.
Sorry for the long post & hope the questions it tries to answer are what you were asking!
Cheers, Liz