There appears to be something missing in the sentence. I also presume that this is actually a poor translation of an original text that was supposed to look something like this:

"I understand that I may revoke this consent in writing, except to the extent that the organization has already taken action in reliance thereon.
http://www.lazarfootcare-spanish.com/docs/2010-english.pdf

Here's a bad translation of the above:
Entiendo que puedo revocar este consentimiento por escrito, excepto en la medida que la organizaron haya tomado sobre la dependencia de esto.
http://www.lazarfootcare-spanish.com/docs/spanish-forms.pdf

Strangely enough, I found another instance of a similar expressions with the end missing here:
I understand that I can revoke this consent in writing, except to the extent that the organization has already taken.
http://houstonwomensclinic.com/Documents/HWC-Forms-English.p...

Odd, huh?

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Note added at 46 mins (2016-04-12 03:52:11 GMT)
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Erratum: **expression**