How to re-register .py file extension to new moved Python dir (on Windows)?

[pstein]

Assume I installed Python v3.1.3 in the default installation directory

C:\Program Files\Python\

Now I decide to move this installation directory (without re-installlation) e.g. to

D:\devtools\Python\

Unfortunately simply moving the installation directory breaks the file associations.
The same applies when I want to use Pything from flash drive.

*.py file association still points to the old directory.
and Environment variable PATH still contains the old Python location too.

So how can I tell Python to re-register itself (for file associations and PATH) by using its current new directory?

Any solution for that?