Been there done that,
Butyrate will go over nitrate but the Butyrate does not have very good sticking power, it is used more for shrinking. I would suggest getting some more nitrate and attach the new fabric.
I have been using nitrate to attach the fabric then use PolyCylic thinned 10-15% with water to fill the weave. It takes about 4-5 light coats lightly sanding after the 2nd coat and each coat after with 400 paper. Pay special attention to you seam areas and add a little extra PolyC to them and be very careful sanding where open structure meets sheeting, it is very easy to sand thru these edges.
If you do it properly the seams will all but disappear.
Good Luck!!
Anthony