maximum dimming percentage

there are at least three ways to do that: Proportion, Curve and scaled Park
Proportion means that every intensity in a cue is multiplied with this factor before being output. values from 1 to 200%.
Curve: you create a new curve where you type 100 @ 50 and then in patch apply this curve to the channel in question
scaled park: in the park display you type Chan 1 @ / 50 Enter. this will half the output value

1 and 2 will automatically be in place when you load that showfile, but not 3.
all 3 will NOT show the reduction in the Live or Blind display. you can see it in the output column of About

ah, and if you want it to dim "regularly" from 0-50 and stay at 50, you would make a curve where you say 50@50 and 100@50. if you only do 100@50 you get a steady dimming from 0-100, but that means with a "normal" dimmer at 50 and the modified one at 50, they won't have the same intensity

So i get the dimming curve idea and that would work if we were not using a profile i guess i should have mentioned this is an RGB Fixture and we are using the generic RGB profile. If only there was a better profile editor to maybe fix a special profile for this need.

If you're just trying to set a 50% limit to the overall intensity of the fixture, then you can still create a custom curve and apply it to that generic RGB fixture as Ueli described. I do this with some LED fixtures I use regularly that behave a little oddly in part of their dimming range. If you were trying to apply this 50% limit to an individual color channel, then it would probably be best to edit the fixture profile.