Not exactly an answer......
Missouri is absolutely anal as regarding their $500./2hr. buy-in limit, including that players may not buy/give/accept chips from each other. Your significant other cannot (legally) give you the rest of his/her chips to play out (at least not on board).
Another nuisance is that your "boarding pass" does not go backwards...for example, if I buy-in at 8am for $500, then at 6pm, decide I want to play for big $, I am not allowed to use my 10am, noon, 2pm, etc. buy-ins, only my 6pm.
In that past I have "hoarded chips", i.e., bought-in when I did not need the chips, and often took them home (for fear of triggering an IRS notice).....this creates other problems....what if you suddenly need some cash $ at home...10 hour round-trip drive to cash-in.
As to your question, I do not know...doubt it would be illegal since I have never signed a "under penalty of perjury" document to get a MO Players card. Exception might be those who are "self-barred"...MO Gaming Commission allows those with Gambling problems to "self-barr" themselves, and they take this very seriously. Might be illegal for these folk to try to play under "false I.D.", however, in this case, the casino might also be liable.
Hopefully others can give you a better answer to your actual question. Most every year now, there is talk of MO lifting its $500 limit, since most serious players go "across the line" to other states that have "no limits". So far though, this has not happened.
phantom007.
