changing the number of parameters may be supported by some DAWs, but I believe not all of the major ones (or plug-in formats) support it.
As for your proposed solution, that sounds reasonable. In our case (different kind of plug-in though), we exposed a fixed set of automation “slots”, each of which could be connected to one of the “internal” parameters at the user discretion.
That ensured max flexibility but the additional level of indirection certainly adds complexity for the user.
If you think some flexibility may be useful in your case, you may follow a similar route but improve its user-friendliness.
For example, the user may choose an automation “colour” for each of the layers, and those colours will be also mentioned in the automated parameters.
So, for example,“Red Volume” will act on the Volume parameter of the layer (if any) marked with the “Red” colour
EDIT: or do a mix of the two: the first 32 (or whatever) layers always have automation parameters, and then 4 or so more sets can be assigned to the layers exceeding 32 via these “colour” markers