If the attribute is still going to be the same for all blocks, then you can change the constant attribute's value within the block definition, and it will update all the rest.
If you want them to be different per insert, then you will have to change it from constant-true to constant-false within the block definition, plus re-insert all the blocks, and erase the old ones.
What are you looking to do exacly? How much experience do you have with writing code?
And Welcome to theSwamp Paul!