How can I trigger a market order stop loss as soon as an indicator reverses at the close of the bar?

I've been using Jeff's universal MA set at 1 EMA and instead of the closing price, I use the 20/3 gaussian filter and that is my stop loss. I use the unirenko set at 3/3 which basically turns it into a momentum bar. A set trailing stop loss has not been very accurate

I am not sure what problem are you trying to solve - are you looking for how to define condition or how to SetStopLoss, or how to execute ExitOrder or maybe something else?

Right now with the super dom the only trailing stop loss I can place is defined by a certain number of ticks.

How can I make the trailing stoploss be the reversal of an indicator?

OK, so your question is really about custom ATM strategy (written in NinjaScript) and this is what you should look for to find an aswer. I am afraid I can't be of much help as this is not an area of my expertise but maybe someone else will chime in.
Since in NT8 you will be able to overlay indicators on the DOM there is a chance this will be possible to set up without coding but don't take my word for it.