LaTeX.org

If this is still relevant for anybody: I found a solution.

Open the .bsp file and search for a function like this:

FUNCTION {format.journal.pages}
{ pages duplicate$ empty$ 'pop$
{ swap$ duplicate$ empty$
{ pop$ pop$ format.pages }
{
", " *
swap$
n.dashify
"pages" bibinfo.check
*
}
if ...