they are technically illegal. they say "For off-road use only" because they are not DOT approved. Doubtful it will make a difference to the cops, unless they truly want to stick you with a ticket!
authentic JDM corner lenses should be dot legal, most of the manufacturers in japan like to cover all their bases, and they usually get them approved by DOT and similar agencies even if they are only intended for the JDM market.
You should be cool with the clears, so long as you use amber bulbs in them.
Interestingly enough, on a black car, like mine, those side markers are a big deal, makes the front-end of your car visible from the sides at night. If they don't have a reflective portion, you should be okay, just remember that if your lights are off, the visibily mentioned earlier will not be as great, not an issue when driving, but nice for when your car is parked in a lot at night, it keeps other drivers from bumpiing into it, especially if your celica is a darker color.
Just some stuff to consider...