Hmmm... Either I don't quite understand what you're saying, or I don't
quite understand what the OP is asking. If I understand the OP correctly:
1. he created paragraph styles named "h1" and "h2", both formatted
with "page break before",
2. he created a footer containing "{styleref "h1"} - { styleref "h2"}",
3. some pages in the document only have "h1" text,
4. the remaining pages in the document have "h2" text and other
text, but no "h1" text,
5. on pages with only "h1" text, he wants the footer to only show
the "h1" text from that page and not show the "h2" text from a preceding
page, and
6. on pages with "h2" text, he wants the footer to show both the
"h1" text from a preceding page and the "h2" text from the current page.

How would a character style help?

Graham Mayor wrote:

How about creating a character style with a unique name and applying that to
the part you wish to call using a STYLEREF field?