Any tips on how to disconnect this connector behind the headlight assembly/housing? It seems that it might need to slide laterally (left/right wrt the car)? Do I have to remove the headlight assembly and/or fender liner, or can I disconnect this in place?

 

The red piece on the right hand side goes further to the right. About 8mm or so. Once you do that the connector will slide out. I use a pick or small screwdriver to gently pry it open. Some dielectric grease will make it easer the second time...

 

Yes, agree. Similar to this connector:

 

Thanks all for your help, I was able to get it disconnected rather easily once I understood how it works. Here are some photos which hopefully help others following my footsteps in addition to BWings' which is probably better: