I've found this your question (albeit lately) looking at the Devs forum space.
I've moved it to a general Forums space, since your question is better to be addressed here.
And here is my suggestion, though I feel it is not what you're expecting to see.
In order to have the Sum of all your Pn Parameter Values equal to 100,
you could have the one of your Pn as a Calculation (100 minus Sum of all others), not a Parameter.
With that in place one could manipulate the other four Parameter Values easily and have all summed up to 100.
Please find the attached.
POC - SC_YF.twbx 41.9 KB