Learn French: S'il avait changé son statut, il se sentirait plus libre. - If he had changed his status, he would feel freer.

This is a mixed conditional. The condition describes a hypothetical situation in the past (s'il avait changé, meaning he didn't change it back then), but the result is how it affects him right now (il se sentirait, meaning he would feel freer today).

Why does si become s'il, and does this elision happen with elle too?

Si only drops its i and uses an apostrophe before il and ils. Before elle or elles, the i remains intact, so you would write si elle avait changé.

Where does the reflexive pronoun go when using a reflexive verb like se sentir in the conditional tense?

Just like in the present tense, the reflexive pronoun (se) goes directly before the conjugated verb (sentirait). If this were a negative sentence, the ne ... pas would wrap around both the pronoun and the verb: il ne se sentirait pas.

How do you know to say plus libre instead of using a specific French word for 'freer'?

French does not have an equivalent to the English '-er' suffix for adjectives. To make a comparative like 'freer', 'taller', or 'faster', you almost always use plus (more) followed by the adjective (libre).