JOSM Undo merge layer

Hi
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?

Edit:
I have created a JOSM ticket for an enhancement in regard to this.
https://josm.openstreetmap.de/ticket/18216#ticket

Edit2:
I have added a ‘Merge selection’ to the toolbar and use from there. This solves my problem. Sorry for the noise.