If using D7, then consider module Views Contextual Filters OR (which only has a dev version today). Excerpt from its project page:
... provides a views plugin which modify query to support OR conditions for contextual filters.
A few issues on Drupal.org that may be of some help:
There is also this comment in the support forum.
StackOverflow.com contains yet another approach to consider as an alternative.
Maybe you should look at Alter a Views query to use "OR" through the user interface also (it might help to change change your mind about the Views Contextual Filters OR module anyway). Because 3,855 reports installs of that module is not nothing, right?
If you're still using D6, then maybe module Views OR is what you are looking for? Excerpt from its project page:
By default, each record in a view must match all filters. Sometimes records need to be included if they match one or more filters in a list of alternatives. Views has the ability to combine filters only with AND. If one filter is false, the combined list will be false. Views Or adds the ability to combine blocks of filters with OR. If one of the filters in the block is true, the combined block will be true.
Note about the "my website is too big" ...
That's perfectly understandable. But that also implies that you should really invest in setting up some kind of testing / staging environment where you have like a mirror of your production environment. So that in THAT environment you can safely experiment / review / finetune what's needed, without impacting your production environment. And after you found the fix in that environment, you should have a process in place to actually MIGRATE it to the production environment ...
A pretty forward (simplistic) approach to this is to transform your existing production site into a multi site setup, whereas you do not change anything to the production site version, but you just add 1 (or more) sites like 'test', 'QA', 'User Acceptance Testing'. These extra sites mostly use the same code base (as production), but with their own copy of the Drupal database. And code changes (or extra modules to be added), first go in site specific subdirs. After they get approved, they are "promoted" to the "all" subdir.