I wrote this post because I saw this question as a top search on my dashboard.
The answer is no. There are several problems with this approach.
1) Crime. That is what this is, Crime. Go to Jail, Do not pass GO, do not collect any $200. You will be characterized as “financial exploiter” at least if you do this in the state named after the first President, and that means you fall under the “slayer statute” and as we all know, slayers do not inherit. Or at least I think we all know this.
2) Breach of Fiduciary duty. There I go again with all that legal stuff. The trouble is that “legal stuff” can get you in trouble, if not in jail, at least sued. Lets say grandma put you on the account “just in case”. It is still not your money. While the bank is authorized to allow you to remove it, the disposition of those funds really have to be for grandma’s benefit and not those who are left here on earth when she passes. She put you on the account because she trusted you, and when we start hearing the word “trust” all kinds of duties attach.
3) Joint Tennant with Right of Survivorship. Lets say grandma opened this account with you and personally, not the bank employee, checked the box that says this or shortened to JTWROS. That is a will substitute that means when she dies the money is yours without probate. Note the timing. It will not be a defense to say that you will inherit this money some day anyway through this non-probate transfer. What if she needs the money before then?
I suspect there are more reasons not to do this but the post is getting too long. You may have good reasons to avoid probate, but this approach is too dangerous. In layman’s terms, don’t take things that don’t belong to you. You don’t have to go to law school to know this. I think we all learned this in kindergarten.