What are these silver stripes on Cosmic Girl for?
It's aluminum "speed tape" being used to run wires around the outside of the fuselage, possibly for load cells or some other kind of sensor related to whatever is being tested and that was impractical to run internally.  If you zoom in the image and look carefully at the vertical strip to the right and below TEST, you can make out a dark line in the middle of the tape that is a shadow from the wire bulging out.  Strictly temporary.

It looks like two window panels have had their acrylic panes removed and replaced with aluminum blanking plates with holes for passing the wire out through the pressure hull, making it a simple job to return to the normal configuration.