The Alarm did a Welsh version of their album, Change, called Newid; which is an easy way to remember this word :)
Typo for yn fawr, no doubt: diolch yn fawr “thank you very much” (cf. mawr “large”).
Is this "change" only in "I want to bring about a change in the world" or also in the sense of "money you receive back after paying too much"?
I've had a look at Gweiadur and apparently it's also used for "a change of clothes" (newid dillad) and "coins of small value" (a pocket full of change) and in am newid "(do something else) for a change".