If you uncheck the file from the file list before committing it won't go into the change set. This means it won't feature in a push (as these are per change set).
This is one feature of Tortoise that makes it useful over the command-line.
If you do a pull with an edited file, you will create multiple heads. You can merge these if you want the file to feature changes, but this might be a manual step.
Alternatively in the case of a config file it is useful to use the Patch Queue functionality of Mercurial. From the command-line this is possible thus (assuming it is changed in your working directory):
hg qnew "localConfig"
hg qrefresh
This creates a new patch queue item called "localConfigs", and puts the edited files (your config file) into the item. You can then:
hg qpop
To remove it from the patch queue (out of your change set path). Or:
hg qpush
To put it in your change set path. This is an easier way of managing file changes that you do regularly on top of keeping pace with the central repository: you pop your queue items out, pull and update, then push the queue items back on (handling any merge conflicts, though these are rare if your items are small). This way you avoid multiple heads.
https://www.mercurial-scm.org/wiki/MqExtension
We tend to use this mechanism in our office.
Note, pushing and popping acts like a stack collection; if "localConfigs" is on top of "moreLocalChanges" you will need both if you wish to push "localConfigs". My example assumes that the "localConfigs" patch is the only one in the queue. It is also disabled by default in Mercurial configuration, but comes bundled with it so you can enable it simply:
[extensions]
mq =
