penumbra
Imperial Masterpiece
Studios all have rules, and for a good reason. I have repaired melt downs because of the wrong clay being used and also seen the consequence of the wrong glazes being used. I see two paths forward for you. First is to get chummy with the owners of the studio you are using and see if you can garner some flexibility based upon your needs. Alternately, look for another studio. Second, it may be time to consider your own kiln so you can take all the time and care you need to go from assemblage to firing. New kilns are the stuff that dreams are made of, but there are plenty of used kilns out there. Best to you in any regard.