Mirror a remote repository in a local branch

[vic]

Hi,

I'd like to keep a mirror of the trunk of a remote directory in a branch 
of my local repository. My use case is that I have made modifications of 
a product for which I have only read access. As the product evolves, I'd 
like to update while keeping my modifications.

I thought of keeping my work in the trunk and the evolutions of the 
remote product in a branch, and merge as necessary, simulating two teams 
working on the same repository.

Is this possible/is there a better way to do this ?

Thanks.