My philosophy is that if it doesn't fit, leave alone
I've had tailors alter things but I'm never entirely happy with the results unless it's just something simple like sleeve shortening
If anybody is in the market for a size 46 (XS) yellow Everest/Antarctic Parka - Flannels in Cardiff have one discounted to around £1000. I was in Cardiff on business today and just happened to stop by.
If interested I would ring the store direct as it's not online because of the fur issue