Can I machine quilt with regular thread on top and my clear thread in my bobbin? I've never tried to quilt with 2 different threads at the same time...

I've used clear on spool & regular in bobbin on my Viking Rose. I don't think I have tired the way you describe.

I mostly use clear thread on spool & bobbin. I have a stitch on my machine that looks like hand stitching when I do applique. With clear on spool, stitch-in-the-ditch is much more forgiving if you waver a bit.

The reason I want the clear on the bottom is so the stitching is less visible on the back on my quilt :)

It is hard to get the invisible thread onto the bobbin. Would it be possible to quilt with the back up? If you are FMQ that should work.

You have to go slower when putting the invisible on bobbin. If you go too fast, it will wrap too tight.

Just for your information, I have recently learn to NOT use clear thread on a child's quilt.

I've used different threads top and bobbin successfully, never invisible thread though

i find using invisible thread on the bobbin is a real pain.
Tension is different and I only use it for wallhangings when I want the quilting to show texture and not new design.
Also, not recommended to use invisible on child's or baby quilts as they could get the ends wrapped around their fingers and cause problems

I still don't understand the part of not using it on a baby/child quilt, have you ever tried to break polyester thread with your hands? I think it could do just as much damage to those little fingers and that's why I try to remember to use cotton for the little one's quilts.

It or any loose thread can wrap around a finger or toe cutting off circulation. On of my dd's got a thread inside a sleeper wrapped around just the tip of her toe as a baby.The tip of her toe was purple and the skin sloughed(?)off. Not permanent damage but had it been down farther she could have lost her toe.The thing with monofilament is you can't see it well.

That said, I have also used it with the "hand"quilting stitch on my machine and do like the wway it looks.