You can easily switch to an Individual selling plan.
Accounts that require a Professional selling plan
If you have a North America Unified Account and your source (primary) marketplace is amazon.com.mx, you are only eligible for a Professional selling plan. You cannot switch to an Individual selling plan.
About North American Unified Accounts
If you have a North America Unified Account and your primary marketplace is amazon.com.br, amazon.com or amazon.ca, you can downgrade your account to an Individual selling plan.
At the end of your current billing cycle, your linked amazon.com.mx account will be placed in staging for 120 days, during which you will no longer be able to sell or have active listings. You will be able to finalize pending transactions during this time, after which the account will be terminated automatically.
Your FBA account for amazon.com.mx will be suspended as well during this process. Please make sure to remove any FBA inventory stored in fulfillment centers in this marketplace before your account becomes inactive.