There's a couple workarounds, although I wouldn't necessarily recommend them.
But you can place your callouts from a Paperspace viewport, in which case they will get moved to Paperspace. Alternately, you can xref your design file into multiple sheet files, and annotate the xref in each.
But we are planning to roll out additional RefNote validations in the future, which will work better if the RefNote is in Modelspace with the design file.
We also have plans to add a RefNote Preferences pane, to enable you to save your callout and arrow preferences. That would be the logical place to also add a checkbox to add a layer suffix for the RefNote Division. This could also apply to all RefNote Objects, providing a tidy way to organize those various plans.

--J

I like where you are going with the refnote preference pane. The ability to separate refnote callouts on separate layers based on division would be very helpful.

I agree with your non-recommendation, that ppspace labeling with refnotes might not be best. I would also prefer not to keynote in ppspace. I understand the pro's of having the annotation sheet specific... but I have found refnotes to be most reliable when everything is in the same design file in modelspace. We make extensive use of the blocks/lengths/areas quantity part of refnotes. I know that the schedule will count blocks that are in an xref... I think the areas will too. The length by layers requires me to change the layer name to have the xref prefix, which makes setting up a template tricky if file names are not exactly the same project to project.

Any timeline for this refnotes pane feature? I know you have a lot on your plate.

Thanks,
Tim

Probably early next year.

--J