Q: Is there any exceptions when it comes to carrying a knife for a convicted felon? Size of knives or multi tool knives?

A: The answer is really based on the definition of a deadly weapon found in RSA 159:3

159:3 Convicted Felons. –

I. A person is guilty of a class B felony if he:

(a) Owns or has in his possession or under his control, a pistol, revolver, or other firearm, or slungshot, metallic knuckles, billies, stiletto, switchblade knife, sword cane, pistol cane, blackjack, dagger, dirk-knife, or other deadly weapon as defined in RSA 625:11, V; and ..

The issue of a bow and arrow was addressed by NH Supreme Court and they said:

A bow and arrow is not one of the enumerated weapons under RSA 159:3, I(a); therefore, to be considered a " deadly weapon" for purposes of that statute, a bow and arrow must fall within the definition of a deadly 158 N.H. 48 weapon under RSA 625:11, V (2007). RSA 625:11, V defines deadly weapon as " any firearm, knife or other substance or thing which, in the manner it is used, intended to be used, or threatened to be used, is known to be capable of producing death or serious bodily injury." Thus, the State was required to prove not only that the defendant possessed the bow and arrow, but that in the manner the defendant used, intended to use, or threatened to use the bow and arrow, it was capable of producing death or serious bodily injury.

State v. Pratte, 158 N.H. 45, 959 A.2d 200 (N.H. 2008)

So the answer is really a maybe you can possess a knife if in the manner it is used so if opening boxes or working on a house the knife is a essentially a tool such as a box cutter.