I don't think you can do that : it's not "the way it works".
If you do not want to be up to date with the branch used by other developpers (the "trunk", generally), a possibility is to create another "branch", on which you'll be the only one working -- this way, it won't be updated unless you merge it with "trunk" ; but it means that, if you want to get some modifications done by the other developpers, you'll have to merge manually between the trunk and your branch, merging only some modifications and not the others... Not sure you'll end up with something working, this way ^^
But you can't work on a file, do an update of your working copy, and have some files be excluded from that update (Anyway, before commiting your changes, you'll have to merge your work with the latest version that's in the repository).