Its really not that bad. I soldered SMT resistors for my older Ballys in the course of a few hours time, but then I am a professional.

470 ohm. I use a fine tweezers and a magnifying lamp. Painstaking, but put some good music on and go to town. I soldered them right to the top of the pinball LED module bulb in parallel with the actual LED. This is the original post I referenced:

"Once upon a time there was a led that flickered when it was installed
in an older Bally or Stern pinball machine. The LEDS flickered on any
machine that used a Bally As2518-14, AS2518-23, or Stern LDB-100. These
lamp driver modules were used from 1977 thru 1989. These boards use SCRs
to switch # 44 Lamps on and off in pinball machines. This has worked
well for many years, until someone tried to use a led instead of a #44
lamp. The LED flickered. I discovered that the reason the led flickered
was that the LED drew no current below it’s forward bias point that it
would not hold an scr latched. If a resistor is added in parallel with
the led, it would draw enough current to keep the scr latched and there
was no flicker. (Life is Good). Through testing I found that a 470 olhm
resistor was more than enough to keep any of the scrs that I tested
latched. The 470 ohm resistor can be added in the socket of the led,
soldered across the lamp socket, or soldered on the lamp driver module.
The electrons don’t know or care where the resistor lives, as long as it
will cause a 1ma load to the anode of the scr. All 3 ways have been done
and they all work well." - text by Ron Googe.