Steam Limiting Account Changes

Steam Database tweets about the discovery of a change in how Steam handles changing the country listed on your account. This is to impede manipulation to take advantage of regional pricing:
In a further crack down on people buying games in cheaper regions, Valve added a limit on how often you can change your Steam account's country.

Country may not be updated more than once every 3 months. Purchases can be completed using a payment method from your current region.