You can definitely have different risk profiles (and therefore portfolios) for each of your Mercer Invest Wise accounts! For example, if you are saving for retirement using your RRSP but are using your TFSA to save for a new car, there is a chance they have different time horizons and probably should be invested in different portfolios!
If you would like to request a change to your portfolio, you are able submit the request here.
Note that your request will require approval from a Portfolio Manager to ensure that your investment changes are aligned with your goals. You may be required to book a call with a Portfolio Manager to ensure that your investment changes are aligned with your goals.