Create new patches with hg qnew patch-name and then update them with new changes with hg qrefresh:
hg qnew myFirstPatch  // Creates a new patch called "myFirstPatch"
...                   // Edit some files
hg qrefresh           // Updates "myFirstPatch" with changes
hg qnew mySecondPatch // Creates a new patch called "mySecondPatch" on top of "myFirstPatch"
...                   // Edid some files
hg qrefresh           // Updates "mySecondPatch" with changes
Create new patch with commit message:
hg qnew -m "My first patch" myFirstPatch
Update commit message of current patch:
hg qrefresh -m "My new message"
Update commit message (multiline) of current patch:
hg qrefresh -e