the whole nandrolone/propecia relationship has been completely misintepreted.
basically it boils down to this
1.) if you're using nandrolone by itself, it has almost no affect on your hairline because its not very androgenic. if you were to propecia to the mix, it converts to a different enzyme that would be a little harsher on your hair (if you're taking deca alone)
now we all know it's stupid to take deca alone for many reasons, so if you're running test + deca + propecia, it's much better and still benefits you than running test + deca w/o propecia because it still greatly neutralizes the effect the DHT from the test has.
In the case of tren, it's so highly androgenic it is normally very harsh on hairlines. you really can't make it worse. i'm not really sure propecia has any benefit, because it doesn't really convert to DHT. it's just the highly androgenic nature of tren will result in hair loss