At a minimum, help text should note this. This is true for things like addwitnessaddress especially.
{
    CWallet * const pwallet = GetWalletForJSONRPCRequest(request);
    if (!EnsureWalletIsAvailable(pwallet, request.fHelp)) {
        return NullUniValue;
    }
    if (request.fHelp || request.params.size() < 1 || request.params.size() > 2)
        throw std::runtime_error(
                            "fundrawtransaction \"hexstring\" ( options )\n"
                            "\nAdd inputs to a transaction until it has enough in value to meet its out value.\n"
                            "This will not modify existing inputs, and will add at most one change output to the outputs.\n"
                            "No existing outputs will be modified unless \"subtractFeeFromOutputs\" is specified.\n"
                            "Note that inputs which were signed may need to be resigned after completion since in/outputs have been added.\n"
                            "The inputs added will not be signed, use signrawtransaction for that.\n"
                            "Note that all existing inputs must have their previous output transaction be in the wallet.\n"
                            "Note that all inputs selected must be of standard form and P2SH scripts must be\n"