Congradulations! I don't think I've ever seen this one asked before, a truely "New" question.
Yes, you can! You probably had excessive settling and now you want to "fill 'er up". By the way, it's also ok to "re-bury" a streched out seedling "somewhat deeper", to give it better support.
If your plant is older and larger, you may want to make a little "Cone" shaped hole around the trunk where you add the new layer of soil, it it makes you feel better. If the trunk is still green, it shouldn't make any difference.
Just scratch around on the old surface to break it loose (don't dig in too much). Then add whatever you're going to add. This would be an excellant opertunity to add lime, fertilizer or whatever else you might want to add.