For those that may be interested in something like this, I installed an illuminated rocker switch on my Moreplay. It works well and is very useful when using metal tubes. I used this exact 4 pin switch:
https://www.amazon.com/dp/B07QQ217DY?psc=1&ref=ppx_yo2ov_dt_b_product_detailsThe color is listed as red but the actual light emitted is more amber colored which matches the tube glow when not using the metal one's which is perfect IMO. It is also the perfect brightness and less intense than the photo indicates.
To install, I did the following:
1. Desolder existing switch and remove.
2. Snap in new switch with "1" facing front of preamp
3. Use existing twisted pair and hook up to one side of switch as shown in attached diagram.
4. Remove existing black wire between transformer T5 and 34U.
5. Install new twisted wire pair to other side of switch as shown in attached diagram.
I would never install one of these on my Crack or S3X amps, the tube glow is obviously the power indicator. Overall very happy with the result. Thanks to Larpy for the idea and PB for wiring guidance from a similar thread in the Crack forum.
Update 11/21/22: I swapped the red switch for a blue one (see photo). Matches the LED's on my power amp better.