Revaluation (Definition):
A calculated adjustment to a country’s official exchange rate relative to a chosen baseline.
The baseline can be anything from wage rates to the price of gold to a foreign currency.
In a fixed exchange rate regime, only a decision by a country’s government (i.e. central bank) can alter the official value of the currency.
Re-denomination has nothing to do with Re-valuation.
When a currency is redenominated the central bank of that country will reissue notes at a decided ratio for both speculators and its citizens.
For ex., If you have a 1000 INR note and Reserve Bank of India (RBI) redenominated at a ratio 1:10 then RBI will take your old 1000 INR note and issue you new 100 INR whose value stays the same. The net value of old 1000 INR will be same as new 100 INR.
The old notes are given certain time period for exchange and then destroyed once they are returned to RBI. Note that, the purchasing power remains the same throughout the transaction except you are getting new notes for old notes.
Differences between Re-denomination & Re-valuation: For re-denomination, All the old notes must be replaced with new notes. This is not needed for a re-valuation.
Re-denomination does not change the net value (Purchasing Power) while Revaluation does that.
Bank should announce in advance for a decision of Re-denomination while banks will never announce in advance for Revaluation.