Is there a way of completely replacing the SQL of a View with my own custom string? Recently I completed a rather complicated View, with plenty of relationships, filters, etc. I needed the View for its elegant page system. Is there a way, after seeing the SQL string, that I complete my string in MySQL, and with minimal change, use it in db_query standard format to replace the SQL string of the View? I know about hook_query_alter and hook_view_query_alter but it is too much abstract than a simple SQL-string, mainly if I already have the string almost complete from the Views UI.
Don't do that. You've got two options: either use Views or don't.

Option 1: Use a custom block/page handler

You can build your own query and theme it any way you want it. Just build it as a block or a custom page and do it the "old-fashioned" way. It will be much cleaner than trying to use views.

Option 2: Use Views

If you want views, then you should build any additional plugins, handlers, or add any alters you need and do it right (that includes using the DB abstraction layer). This isn't hard and there is plenty of documentation floating around that can help you with this.

If you circumvent the systems you have (e.g. Views), you will end up producing code that isn't maintainable by someone else or could unknowingly introduce problems. Please don't look for shortcuts, do it well and do it right.