Using a modified chip or cabin with more than 10 AGs is possible and parts let you select them (for example the interstage connecting the LES to the cabin id=845)

Select part 845 and assign AG21 (it's named Cabin Landing)
Save the craft and load it again, now part 845 has AG20 assigned.

Even trying to force >21 values to be used by the part seems to be broken

Bug Active Found in 0.8.106.0
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