How do I change any page to a different page style?

writer
version 5.1.3.2

A page style does not apply to a single visual page, but to a continuous part of text, as long as no manual page break is inserted explicitly changing the page style.

‘Insert’ > ‘Manual Break…’ > ‘Page break’ > Choose style

The new style must exist (be created) in advance as a named style for the purpose.