I’m not sure I understand your total process with RM and citations, but I think I can make a few comments.
First of all, if you are using Zotero footnotes and copying them into RM, there are a couple of ways you can do it. One way is that you can copy them into RM’s free form source template. If you do copy them into RM’s free form template, there are two fields, namely Footnote and Page Number. Despite its name, the Footnote field is not the complete footnote. Rather, the complete footnote is the concatenation of the Footnote field and the Page Number field. So you might need to divide your Zotero footnote between RM’s Footnote field and RM’s Page Number field.
The other way is that regardless of which source template you are using in RM, you can paste a completed footnote into RM by using the Customize feature.
The customized footnote replaces whatever footnote would have been created via the data you entered into either the Footnote field or the Page Number field.
No matter how you do your footnotes in RM, the way RM and essentially all other desktop genealogy software does it it there ends up being two fields. I sometimes like to call the two fields the left part and right part of the footnote. I would call them the left half and the right half of the footnote, but sometimes the two “halves” are not really the same size. They manifest themselves in RM’s source and citation screens as Master Source and Source Details.
RM’s free form source template also has a Bibliography field that you an fill in any way you wish. It is a Master Source field. It is shared by all citations that share the same Master Source. RM’s customized citation feature likely contains text from what you might consider both left part and right part information, but it is stored and managed as part of the Source Details or right part data. But it prints as the whole citation. So you could customize both the bibliography and also the whole footnote.
I do my sources and citation totally from within RM rather than using an external source and citation manager such as Zotero. But if I were using Zotero, I suspect first of all that I would use RM’s free form template. Any of RM’s actual source templates would just be getting in my way if I were using Zotero. Then I would make my source name and bibliography in the Master Source be an appropriate left part of the Zotero footnote. And I would make my citation name be an appropriate right part of the Zotero footnote.