Basically, it seems that I need an svn analog of the git feature, pointed out in this post.
Here are my requirments.
I have a branch where I need to make some local changes on a file but never want to commit them so I'd like ot ignore them, but still keep the file versioned and be able integrate changes from trunk (so differently as here). As I understood correctly the command svn propset svn:ignore "file.ext" . (cp. this post) would unversion the file completely. And this state wuld be commited to the branch and eventually to the trunk when merged. (The same would be when applying "unversion and add to the ignore list" when using TortoiseSVN GUI, I suppose.) So I would need something else in this particular case. Please, give also examples for TortoiseSVN, if possible.
I use Subversion 1.11.1 on the server, Subversion 1.14.1 on the local machine and TortoiseSVN 1.14.1 respectively.
Use the ignore-on-commit changelist with TortoiseSVN. See TortoiseSVN Manual | Excluding Items from the Commit List.