Is there any reason I shouldn't proactively add the proportionate amount of vermouth to a half-empty bottle of gin? (vs, best)

[Those Who Squirm]

While mixing a martini last night, I began to wonder if there's any reason I can't simply add vermouth into the gin bottle, so the next time I'd need to bring out only one bottle and simply pour the necessary amount of gin/vermouth mixture into the shaker.

To provide the appropriate context:

1. I only use the gin for martinis.
2. The gin is kept in the freezer.
3. I usually mix martinis at about a 3.5 ratio gin:vermouth.
4. I usually use regular 80-proof Bombay or similar.
5. I might take a week or two to finish off the martini mixture (wife prefers vodka so I'm the only one using the gin).

Are there any drawbacks to keeping a martini mixture in the freezer long term? As the mixture sits in the freezer for days or weeks, could either ingredient react to the other in some way that would spoil the product?

[Gerania]

Not that I know of. It's going to be kept cold.

https://www.seriouseats.com/best-way...ver-rebottling

[steiconi]

My dad always did this. I believe he used a mix of gin, vodka, and vermouth.

[Nodpete]

We always used 90 proof or better gin. mixed 3 oz. gin to 3 drops of a good vermouth. Yes I used an eyedropper. First one was super, second one was even better, third one must have been good or I wouldn't have drank it, finally gave them up several years ago.