Whoa, a new feature!

Sequence Editor: SHIFT+R, Remap Paths (also in pull down menu)

This allows to remap the root of a path to another directory.
Works on all selected Image strips. That way you can make absolute
paths relative, for example.

Example:
original path: /mnt/orange/finals/06_which_way/06_03b/
to be remapped: /mnt/orange/finals/
remap to: //
new path: //06_which_way/06_03b/

source/blender/src/space.c

@@ -4473,7 +4473,10 @@ static void winqreadseqspace(ScrArea *sa, void *spacedata, BWinEvent *evt)
 			}
 			break;
 		case RKEY:
-			reassign_inputs_seq_effect();
+			if((G.qual==LR_SHIFTKEY))
+				seq_remap_paths();
+			else
+				reassign_inputs_seq_effect();
 			break;
 		case SKEY:
 			if((G.qual==LR_SHIFTKEY))