It would be easier to ADD a relay, SPST. If you try to energize the installed relay, you will have to isolate it with a pair of diodes to avoid turning on other electrical items when you open the door.
I have done similar with MANY of my Subaru's so I can operate the windows in ACC instead of just the ON key position. Connect the contact points to an ALWAYS on power source like the power window fuse or Circuit breaker, the other side to the power feed wire going to the power window switch. Then attach one side of the coil to your ALWAYS on you just used on the contact point and attach the other side of the coil to the door switch which will ground and energize the relay when the door is opened. This way there is NO feedback of power to any other devices when you open the door.
These are the relays I used ....... https://www.amazon.com/gp/product/B01KH17YKU/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1