JOSM Undo merge layer

I have been updating some multipolygons and accidentally selected ‘merge layer’ instead of ‘merge selected’
I have not uploaded yet and wish to undo the ‘merge layer’ action and continue editing instead of aborting the session and starting again.
Can I undo a merge action?

I have created a JOSM ticket for an enhancement in regard to this.

I have added a ‘Merge selection’ to the toolbar and use from there. This solves my problem. Sorry for the noise.