If you want to go down to 12′s, you have 2 Elixir options:
Light-Medium – 12 / 56 – same 3 bass string gauges as Medium, but lighter top 3 strings, or
Light – 12 / 53 – all 6 strings are lighter than Medium.

I’ve experimented with different gauge strings on my Taylor 914ce’s and 655 (and other guitars over the years).

I’ve rarely (never on my 914ce’s) had to make any adjustment to saddle or nut grooves.

I’ve found this impacts 3 things – tone, intonation, and playability. I assume it would be similar for the GS7…

The easiest one to discuss is tone…With lighter strings, the tone is generally, well, lighter! By that I mean a “thinner” high end and loss of bass depth. But the impact is different when you play acoustic vs electro-acoustic. You can compensate for both of these if you play electro.

Whether intonation is an issue for you and your audience depends a bit on your playing style. I found that moving to lighter strings, I was more likely to apply too much left-hand pressure, resulting in sharpened fretted notes, especially on the bass strings.

Lighter strings take less left hand effort, so generally enhances playability, and makes pulling and pushing much less hard work on an acoustic guitar. However, with a light top E-string, I found I sometimes slid the string off the edge of the finger board, until I got used to the lighter strings.

The other issue you may find with fitting lighter (therefore looser) strings is increased fret-buzz. Again, depends on your playing style – unlikely to be an issue for finger style use.

Personally, I prefer the light-medium combination – retains the richer bass, avoids left-hand induced intonation problems, but makes it easier to pull/push the treble strings.

I’d suggest leaving any truss rod adjustment until you settle on the gauge you prefer, then adjust, if necessary to optimize action and minimize fretbuzz.

Many thanks.