Is your feature request related to a problem? Please describe.
It has always been a cause for frustration for me to edit the schematic to replace a certain block with another block (e.g replacing cobblestone stairs with stone bricks stairs)
The idea of going to the "Edit Schematic" mode and then having a keybind to pick the block I wanna replace with the block on my hand is simply tedious. Not to mention the fact that if you rejoin the server/enter a new dimension and then come back all the editing of the schematic has been undone and you have to start all over again.

Describe the solution you'd like
The solution I'd like is simple. When opening the material list you should see a 'Replace' button beside the 'Ignore' button like so.

After clicking the 'Replace' button you'll be greeted with a comprehensive list for all of minecraft blocks or atleast blocks that can match the original block's state.

And a button that can revert all the edits done.

Describe alternatives you've considered
An alternate solution is to simply atleast remember the edits that the user made to the schematic instead of forgetting it the moment the rejoin the server/enter a new dimension.