Short answer: they are effectively fixed after creation
Currency and time zone are set when a Meta ad account is created, and Ads Manager generally offers no field to edit them afterwards. The usual workaround is to open a new ad account and move audiences, creatives and pixel access over. Whether any exception exists depends on what Meta's help pages and your account show at the time, so don't build a purchase plan around someone else's one-off fix. Checking both before you buy is far cheaper than repairing later.
Currency affects more than the number on screen
Currency sets the unit for budgets and bids, the billing amounts, which payment methods are usable, and how finance reconciles spend. Charging a card in a foreign currency may add conversion and fees, depending on the issuer. Minimum daily budgets also differ by currency, so a small test budget should be checked against the minimum the account actually displays, not against experience from another currency.
Time zone controls reporting cutoffs and pacing
The time zone decides when each reporting day starts, when daily budgets reset, and what "yesterday" means in reports. If it sits far from your market, daily reports won't line up with local sales days and scheduled delivery needs manual conversion. If you use a third-party dashboard, confirm whether it reads the account time zone or its own setting, or the same day's spend will differ between tools.
A pre-purchase comparison checklist
Check these: the main settlement currency of your target country versus the account currency; whether your payment method supports that currency; the time difference between the account and where conversions happen; whether finance needs local-currency invoicing; and whether other accounts already run in the same market and need consistent reporting. If two or more don't match, pick a different account rather than buying and hoping to adjust.
Existing accounts carry history in the old setup
When taking over a used account, remember its spend, audiences and pixel data accumulated under the old currency and time zone. The data isn't wrong, but attribution and reconciliation need extra conversion. If you want to reuse learning data, confirm it still applies to your new market. If you only want account age, matching currency and time zone matters more.
When to stop and choose another account
Walk away if the seller can't say which currency and time zone were chosen, if screenshots contradict what they told you, if your payment method doesn't support the currency, or if the account is restricted and the seller avoids explaining. None of these can be fixed by changing settings after purchase. Rely on what you see after logging in, not on verbal descriptions.