Lighting a JetRanger off with the MR still tied down should pose no big problems. You'll notice it soon enough. ...Or at least, you *should* notice it. I've known one or two oblivious pilots who got the bloody thing nearly all the way up to idle before they realized something was amiss. If the tiedown rope/strap breaks things can get...um, interesting and you're probably bug*ered. I've heard about 206's torqued completely over onto their side (strong C-20's!). And I actually saw one that *nearly* went over. It lifted its skid a bit, then dropped it back down hard enough to wrinkle skin (the aircraft's, not the pilot's). If nothing else, the remaining strap ends are GOING to cause some damage as they flail around while you're trying to pump the rotor brake as fast as you can.
I know that what I'm saying next will go against the grain, but I never did subscribe to that "put the blade 90 degrees" stuff. For one thing, it persuades you to forget about the main rotor for the time being and focusing completely inside the cockpit during the start. Wrong!
Here's the other reason: The RFM says that the MR must be turning by 25% N1. If you cannot see the blade, how do you know it is turning? New 206 pilots are usually so overwhelmed by the process that they cannot give a quick glance up to check that the blade has started to turn, but after awhile it shouldn't be all that much of a challenge. In the GOM awhile back, I did catch one engine that my "opposite" had been short-cooling. The MR didn't even budge by 30% N1. I turned the rotor backward enough to actually start to take hours *off* the Hobbsmeter, but to no avail; the mechs had to change the turbine. Had I been one to put the blades athwart, I might not have noticed right away.
Oh, and starting with the fuel valve off is no big deal. If you have a C-20B and you're watching closely, you'll see the TOT start to waver a bit just before it signs off. (This should clue you in so that you won't be surprised next time you do it.) If you're quick, simply keep the button depressed with one hand while quickly flipping the valve on with the other. The engine will re-light and you can continue on your merry way. I've never had...um, I mean I'VE NEVER HEARD OF a C-20B "going hot" if you do this, although it's certainly something I watch...I mean IT WOULD CERTAINLY BE something I'd watch for. (A C-30 is trickier. It doesn't give you the little needle fluctuation that the -20 does.)
Starting with the throttle open can be REAL exciting (and expensive). Fortunately I have never performed this particular trick (yet). Check throttle closed! Then check it again. And a third time. Then one final time just before punching the button. And if you can't remember doing it, do it. There is no danger, and despite what some people say, you *cannot* introduce raw fuel into the combustion chamber by doing this as long as everything is working properly.
Do not ask me how I know any of this. I'd have to kill you. But let's just say that I've been flying 206's longer than I care to admit, and have made just about every mistake imagineable...and some that Bell probably hadn't imagined. I did get into advancing blade stall one day...but that's another story.