Am I correct in that you would enforce a single concrete
citation format throughout the document that way?

 You were asking for comments
about your solution, I hope the following remarks are informative to
you.

My .bib file is being autogenerated by Mendeley, a reference manager,
and changes often in terms of contents. That workflow seems
incompatible with your solution. Furthermore, I may not let the
authors appear in citations with all their names every time, it should
be limited to the first time (the APA 6 rules, that I referred to).
With your solution, 1 out of n citations would be correct, while in
the current situation (without manual intervention) n-1 out of n would
be correct (all but the first).

 I clearly misunderstood your problem, which, as I see now, thanks to your remarks, is rather different from mine. 

I would not have sent you my silly answer if I had known this.

On the other hand, I too need citations and bibliographic references to appear in different forms, three in my case:

In the Bibliography with Author: Last name, first name, 

In the text and footnotes the first time with Author(s): First name(s), last name(s),  and full title of the work, and in all the following citations with Author(s): Last name(s) only and short title of the work. 

I could think of no other way to accomplish this than to generate the .bbl, make two copies, “Inversed Author” and “Short Title”, make the necessary changes in these .bbl’s, including the cite-key to mark it for these two alternatives. I should add that I could not use apa  but an apa-like, modified in many details which also forced me to tweak the .bbl.

It all seems a lot of work but it is straightforward, it works for me and it protects me from an enormous amount of frustration.

(And I’m glad my .bib-file is not autogenerated.)

Best regards,

Robert Blackstone