cloning files without tracking changes

[Nenad Bulatovic]

Hi
Does Mercurial have some kind of mechanism to prevent certain files in 
repository from being modified?
More precisely  - I need some files cloned from the repository, but I don't 
want to track the changes in those files.
When I do a 'hg add' on all files from my (very large) source tree, I need 
some files in the repository to be intact (because, for example, build 
process modifies them) and I want to have a clean changeset with files that 
only I have modified.
Is something like this possible?