modal auxiliaries are specialized towards the expression of certain speech act

[suprunp]

From the semantic point of view, modal auxiliaries are often specialized
towards the expression of certain speech acts; eg giving advice (ought to,
should), making promises or threats (will), giving orders (must, can), etc.

(A Comprehensive Grammar of the English Language)

Have I understood the part in bold?

Certain speech acts can be expressed through modal auxiliaries.

Thanks.

[Tdol]

Yes, though I'd reverse the order:
Modal auxiliaries can express certain speech acts.