In hg (or any DVCS) you can combine any set of changes with any other set of changes (except for the ancestors). If you open the repository log from TortoiseHG (View Changelog from the Explorer context menu or hgtk logfrom the command line), you can update it to any set of changes, then select "merge with".
In your particular case, you are updated to the head of your branch, and then merge with the head of the trunk.
source
share