How do i subscribe to an OPML file from a blog aggregator in google reader. I can import the file, but its a one-time operation and does not keep up with changes in the opml file
OPML is only here to describe a list of RSS / Atom stream.
Then this is a one-time operation and future changes update should be managed by the RSS/Atom links in the OPML. (You subscribe to all the RSS in the OPML file)
Are the RSS valids?
You can try the export function and look at the file if you'd like. It's just a mean to create a "playlist" of RSS links.