I'm not really familiar with all options that local branch can have, but there is for sure:

• remote tracking branch - branch can but does not have to track remote branch
• I think push command can be controled also.
• maybe more...

so maybe branches dialog could get another pushbutton - "branch options", where user could modify options for remote tracking branch and push command.

aditionally, when creating branches there is already option to set remote trackied branch, but maybe this can be modified from checkbox to a combobox, with pre-selected option from a dialog. This way if user does not preselect remote branch, it can still be set. Of course, it would be nice to be able to set push command for a branch here too.

IMO this dialog with branch properties and create branch popup should essentially be the same thing, only used in two ways - when creating branch and to modify existing branch properties.