I'm not a big fan of dry tanning for the long run.....
Can dry tanned/frozen otter hides be re-tanned or made more
stable somehow?
I guess I have to assume that when you say "dry tan" you mean dry preservatives. And hopefully I've assumed correctly. If this is true, then yes, they can be retanned - but first they must be rehydrated, and pickled! The rehydration is the tricky part. Dry Preservatives typically contain Borax and other alkaline (high Ph) materials. If the skins stay in the soak too long they may be lose some fur. The epidermis will weaken. Once they are softened however, they can then be pickled and tanned. You will have to watch them in the pickle too! More than likely some of the dry preservative was absorbed by the skins and you may have to compensate for this by frequently checking the pickle's Ph level, and readjusting it by using more acid. Leave the skins in the acid longer then usual. That way, once your pickle remains stable for 2-3 days, you can also safely assume the skins are readjusted Ph wise, and can now be safely tanned. Myself - I'd use our Rittels EZ-100 for retanning - but you may also have a personal preference.
Only info from supplier is that the otter is dry tanned
so I'll also assume...but you know what they say!
I am indeed a satisfied user of EZ and have been for a while.
Your expertise is very much appreciated.