If memory serves, an altered license can be rejected by anyone who is attempting to utilize it to verify things like proof of age (for purposes of purchasing alcohol) or your identity for purposes of accepting checks. Your date of birth and driver's license number are not particularly sensitive pieces of information. Every check you write (assuming you write checks) probably gets your driver's license number written on it. If you need to rent a car, car rental companies routinely make a copy of your driver's license. So I do not recommend altering your license to block out information, as it is likely to produce all sorts of results you don't intend.
Not legal advice, just my two cents. I don't practice law in California or hold California licensure. If you need legal advice, please consult a lawyer who holds California licensure. That's not me as I practice in Vermont ONLY.
Do not modify your drivers license. Make a phtocopy and alter the photocopy. If the conservator wants to compare the original to the photocopy, that should not be a problem.
The above is general legal and business analysis. It is not "legal advice" but analysis, and different lawyers may analyse this matter differently, especially if there are additional facts not reflected in the question. I am not your attorney until retained by a written retainer agreement signed by both of us. I am only licensed in California. See also avvo.com terms and conditions item 9, incorporated as if it was reprinted here.
Give them a copy of your proof of insurance.
Make a copy of your license and block out some of the information on the copy, and you can show them the original license, but ask them not to write the info down.
If that is not good enough for them, then stop driving your friend.
Disclaimer: The materials provided below are informational and should not be relied upon as legal advice.
As attorney Doland properly states, make a photo copy and then redact the sensitive information on the copy. Depending on whether your friend's conservator is a trustworthy person and whether she/he is able to keep the license copy in a safe, inaccessible location, you will be wise to redact sensitive information such as date of birth, your signature, license number, etc. Perhaps you can ask this conservator if she/he will be satisfied viewing your license without needing to keep a copy of it. Be sure to consult your own attorney to protect your legal rights.
Normally these questions come up concerning a retail transaction. Based on the duties and responsibilities of a Conservator, I don't find their request to be unreasonable in regard to your driver's license and insurance policy. I would do the same. They may be concerned about your date of birth which would be reasonable in their capacity as Conservator. It seems like if you take exception to this request, the simple solution is do not drive your girlfriend around.
I hope this is helpful.
John N. Kitta
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