It is a gray area at best and to begin with it does depend upon the foundry from whom you've licensed the typeface. Have you licensed the typeface already? Can you tell us the foundry?

No, I dont know what typeface I'm going to use=)
Speaking of which, can anyone recommend something bold, rounded, with or without inktraps...?

Usually, you are prohibited from taking a font you have licensed and using its outlines and other data to make another, whether that new creation is very similar or very distinct from the original. You can typically modify the outlines of the font in a program like Illustrator, but you usually cannot make a font out of your modifications. You can usually create a new font based on a previous design if the original is a printed specimen, i.e. not first created in digital form.

I've emphasized that this is what I believe many (not all) EULAs require, but as Tiffany said, you should examine the license agreement of the foundry you are considering licensing the font from and e-mail or call them if you have any questions.

As for the recommendation, you should try searching Typophile first (I know I've seen a thread about rounded type recently) and then make a new post in General Discussions if you want more or more specific recommendations.

I'll add that 99.9% if not 100% of foundries do not allow derivate work to be sold as a new and/or original font. From that, most foundries don't even allow modification. However, some foundries, such as Adobe, do allow you to modify their fonts and use them internally for other work.

I see. But what if there's no certain way of telling what typeface that has been modified?=)

In that case you should not ask here.

. . .
Bert Vanderveen BNO

Why don’t you design a typeface for it?

Your rights are determined by law. If they're important, don't rely on foundries or font designers for legal advice.

don’t rely on foundries or font designers for legal advice.
in this case...wrong.
If you are modifying a font or thinking about modifying a font, you MUST rely on the foundry's EULA. Legally that is the contract between the foundry or designer and the end user or potential modifier.