imakeidx and api to personalize reference system

Maïeul, I did not go into the details, but what you are asking for appears to be already available in eledmac with the command \edindex (see pages 28-29 of the eledmac documentation), that accepts an optional argument as per the symtax of memoir, which is identical to the syntax of imakeidx: [tt]\edindex[file]{index entry}[/tt].

I never used eledmac, and I don’t even know how to use it, because I do not write any critical edition, and I have no suitable text to try to use it with. But you do, and did you try [tt]\edindex[/tt]?

But did you try to use \edindex[file]{index entry} without the class memoir? I told you that imakeidx uses the same syntax of memoir, so that apparently \eindex should behave the same even without memoir. Is I told you I have no sample text to test what I am saying. but you can easilly test it; let us know what’s going wrong if something goes wrong.