Ive been trying for a few hours trying to get a shiny registeel and so far nothing...
Yes you can.
Although the frames on which a shiny will appear will be exactly the same no matter how many times you soft reset. So if you keep resetting and activate Registeel the same length of time between resets you will not get a shiny. The best way to go from here is to activate the Registeel after playing for a little each time.
It's going to be a very tedious task, but good luck to you.
Sources: Internal battery affects clock based events and I caught most of my shines with a battery-dry Diamond.