You asked if it would be "ok" to do those mods. My answer was no, it would not be ok. If you can somehow hide the fact that you have done these mods when you return the car, then you might get away with it, but that doesn't mean it was ok. Sort of like "Is it ok to rob a bank?" No it isn't, but if you don't get caught there might not be any consequences.
2008 Sparkling Graphite 535i
2009 Land Rover LR2
2003 Porsche 911 Turbo (SOLD)
2006 Jet Black 325i (SOLD)
2001 Bullitt Mustang (450rwhp - SOLD)