Q: vector map patching

Hi,

currently I have the problem to merge a small vector map
in good digitizing quality and a second in less quality.
The small one is part of the second - I want to *replace*
a part of the map with less quality by overlaying this
small map:

-------------
|less qual. |
| |
| |
| |----| |
| |good| |
| |qual| |
-------------

How to perform such replacement in GRASS? I feel that v.patch
will just overlay both maps.

Thanks for assistance

   Markus