forecasting custom universal pollers?

All of those alert leverage the fact that SolarWinds has built in tables specifically for calculating those rates of change and forecasting them out. Since those tables don't exist for UNDP's you basically need to do the math yourself with custom SQL. Depending on how advanced you want to get into the statistics you could do something like just compare a value from a month ago the most recent stat, divide by the number of days for a rate of change. In practice I bet you would want something a little more accurate than that, but fortunately there's tons of data out there about how to do robust forecasting in SQL
https://www.sqlservercentral.com/articles/forecasting-with-sql