No... if you fill in the bid amount box, but don't submit it (it actually takes two actions to complete the submission, there's a following box that asks you to confirm your bid) no one, especailly the seller will be able to see that you've terminated you inclination to bid but didn't follow through.
By the way, this applies to the E-bay system as displayed here in the U.S., but I suspect it's the same, pretty much, worldwide...
As someone has already alluded... once a bid has been made on any item, the price posted by the seller cannot be changed. However, even after a posted bid, you can "early terminate" the sale and then complete the entire process to re-list the item. I don't think E-bay appreciates this kind of manipulation, but then I've never used that function...