When a neutron converts itself into a proton, a negative quark changes into a positive quark. As the positive charge is geather than the negative ofcourse we must account for the expelled electron, it seems as there is a creation of charge and anticharge and maybe the nucleon quark charge is a resultant charge made up of distinct quantities of positive and negative charges in superposition. Are in that case quarks composite particles?
We don't use "anticharge" when discussing electric charge, because there are matter particles with positive charge and also matter particles with negative charge.
Quarks come in "flavors" whose electric charges are one unit apart, but which are not equal in magnitude. The "up"-type quarks (called "up," "charm," and "top") have electric charge $+2/3$, while the down-type quarks ("down," "strange," "bottom") have electric charge $-1/3$. In a charged weak decay, a down-type quark changes into an up-type quark (or vice-versa); electric charge is conserved by emitting a charged lepton (an electron, a muon, or a tau) and a neutrino.
All of these particles have antimatter counterparts, whose electric charge is equal and opposite to the matter particle. So an anti-up quark has electric charge $-2/3$, and an anti-down quark has electric charge $+1/3$. Antiquarks are not involved in the beta decay of the matter neutron (well, not at "tree level").
There is a technical distinction between a particle that is a "superposition" and a particle that is "composite." There is currently no evidence that quarks are composite, with a substructure, in the way that atoms are composed of well-defined other particles. But there are several non-composite particles which can fairly be described as superpositions. Examples include the neutral $K$ mesons$^\dagger$; the neutrinos, whose flavor states don't have a well-defined mass and whose mass states don't have a well-defined flavor; and the photon, which is a mixture of two particles (which cannot be observed on their own) called $W^0$ and $B$.
$^\dagger$ Oops, the $K$ mesons are composite, since they're made of quarks. But if you want to read more about what a superposition means, the literature on $K$ mesons is a good place to start.