Noteman says: To automatically modify the appearance of all beams at once, use the Patterson Beams plug-in.

Beaming of eighth notes (and notes of smaller value) is automatic in Finale, although you can override Finale’s beaming decisions, either on a global, regional, or case-by-case basis.

See also:

Beam angles

Beam thickness

Beaming across barlines

Beaming over rests

Beaming: feathered beaming

Beaming: secondary beams