Modify files in start-commit

Is it possible to modify files in a start-commit hook and include them with a commit?

We have multiple components here in the same svn tree, and we'd like to bump a release number on each one as commits occur. Rather than trying to add code to check how many commits have been made to the area at build time, I'm considering whether it would be possible to have a hook script edit a VERSION file under the affected commponent area, incrementing a number in there by 1 and including that file in the commit.

Is that actually possible, or would I instead have to force the developers to aways modify the file VERSION and check for it's present in the transaction?

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Regards,
Darragh Bailey
Systems Software Engineer
Hewlett Packard Galway Ltd.
Postal Address:    Hewlett Packard Galway Limited, Ballybrit Business Park, Galway
Registered Office: Hewlett Packard Galway Limited, 63-74 Sir John Rogerson's Quay Dublin 2
Registered Number: 361933