You're reading the Knox translation. Nisbet (the more recent Cambridge translation) translates as follows
It is impossible to break into the inner conviction of human beings; it is inviolable, and the moral will is therefore inaccessible. The worth of a human is measured by his inward actions, and hence the point of view of morality is that of freedom which has being for it self.
I think a good question here is why Hegel writes this as assertion. To decipher this, we need to look at a few things at once and consider these theories.
First, as an Addition, the remarks are meant as a comment on section 106 to expand on section 106 itself, which claims "subjectivity now constitutes the determinacy of the concept and is distinct from the concept as such..."
The "now" hints that this is a moment in Hegel's dialectical logic. What sort of moment? This is almost immediately after the end of the section abstract right (abstrakte Rechte). There, Hegel is looking at something roughly like our concept of rights but in abstraction from a system of law or society. Motivated by the problem Unrecht, this leads to "civil society" wherein rights are granted a social and legal existence that we will learn is incomplete.
Moving more broadly within Hegel, we can note that Hegel is referencing the "concept." The concept [der Begriff] is a term for that which Geist comprehends in all of its distinctions. Thus, a big part of what is going on in here is that in Moralitaet the concept is taking on subjective form, because as Hegel has stated earlier on freedom, reason, and will are for him identical. At the point of this passage, the case is not fully distinguished, but the bald manner in which the addition asserts it makes it seem like Hegel does it take it to be quintissential to the self to have complete control over will.
Further in the text, this subjectivity is joined to a more robust idea of community and freedom, but I'm not aware of anywhere in which Hegel denies the idea that human selves qua rational beings have control over their inner convictions (a position that sounds thoroughly Kantian and Cartesian to me).