Video editing in mediocre hardware I was thinking of an idea to edit full HD videos in mediocre hardware. Firstly downscale entire video clips to a lower resolution eg. 640px. Edit and play around with these low res clips. Then let the computer repeat these on high resolution clips overnight (undisturbed).

This there such an option or is it possible using a python script ?
Proxy feature is designed for that purpose, make it easier to edit heavy video sequences. Generate 25% proxies of your strips, use those for editing (by choosing them as Proxy render size option of the View Settings panel), and you are done. Original files will be used automatically for final render.

See the manual for more details.