Here’s an example of one of my mulberry T-buds this summer, Morus nigra “Persian,” where I removed the rootstock branch about 2 weeks ago after the bud had callused, which successfully forced it:
I did that bud a month ago, posted photos here then:
If I had a larger tree that I wanted to graft over at this time of year, I’d do the same thing on all the branches and then just completely remove any that fail.