I have to make local changes to my project files in order to get it to run in a different environment. Twice now I accidentally checked those changes in (and messed up ever
What client do you use?
TortoiseSVN has a nifty feature that takes advantage of the changelist feature built into SVN. If you right click on a modified folder and choose "Check for Modifications," you can right-click on any of the modified files in that dialog and choose "Add to Changelist -> ignore-on-commit." From then on, whenever you perform a commit Tortoise makes sure not to add those files to the commit. See "Excluding Items from the Commit List" on this page.
If you're not using tortoise, you could set up a similar changelist manually.