Should I file an amended return if I filed for 2018 and then received a Form 1041 Schedule K-1 resulting in no change in federal tax and a $64 refund in CA state tax?

Well, there is certainly no need to amend your federal return. It is up to you whether or not you file an amended return for California. It is not required in any way.

Please be aware that, due to the IRS matching system, you may receive a notice.  If this does happen, you can respond with a simple letter that states that the amendment does not affect your taxable income so no amended return was filed and send that back with a copy of your new tax form.