svn checkin from tag to trunk

svn checkin from tag to trunk

We maintain our SVN database as a single trunk, with no branches on a
day-to-day basis.
We do, however, tag stable 'releases' from time to time. These tags are
really intended to be tags, meaning no one checks anything in to tags.
Now, the way we intend to work is when there is a bug, a user checks out a
given "Golden" tag (a working database) makes edits to their files and
these changes need to go back into trunk.
I have tried in vain to figure out a way to do this.
svn switch won't work since it updates the local working copy (which I do
not want). svn merge isn't working either since it appears to check in
changes to the tag before merging them to the trunk, as well as have 2
versions checked out - trunk and tag.
The only way I see this working is to actually have 2 checked out
databases and physically copy over files from tag to trunk (perhaps merge
will also work at that point, but that defeats the purpose)
Technically I do not need a merge either. In fact, I would prefer to
check-in files directly, rather than merge, since I know what I am doing
in this particular case and conflicts can arise with a merge during
compile (not standard C or software code!). What I need is an easy way to
switch my SVN url from tag to trunk non-destructively - i.e - nothing
changes but the URL. No updates or anything.
Failing that, I would prefer a way to check in a file from a tag-check-out
directly into trunk.
Any ideas anyone?
Thanks in advance MicRavi