When trying to insert a custom time signature in my Flow…it seems to want to destroy most of the material in that Flow…before that point…what am I doing wrong?..please advise. Thanks.
How do you mean “wants to destroy”?
If you mean it rebars everything, then you need to set a (initially redudant) time signature where you want the normal time to resume and only then insert your custom signature.
Whether Insert Mode is active makes a difference too, so you may want to do an experiment (proof of concept) on a small file or copy of your actual file before working on your actual file.