Do the whole panel lamp fittings need replacing because of their condition, or could you get away with fitting LED versions of the bulbs?
My hazy memory of equipment standards is that indicator lamp requirements would be included in the applicable product standard. There certainly are rules about what colour you can use for what, especially in medical!
Although related to safety, I don't think BMS comes into the 'safety critical' category.
There's bound to be a BSEN nnnn on panel lamps, but after investing £100 it probably won't tell you anything you don't know already.
Edit BS EN 60204-1 Machinery and BS EN 60073 Man/machine interface coding principles for indicators ?
There's the usual caveat about your liability when you start modifying equipment, but it's presumably bespoke hardware already, so not much different from normal?