Day 13 rune script:
I, (the runemaster), carve a path through the icy wastes - Isa(Raido) 10, Method II - causes ice to melt within ten paces of the ship or cart that the runes are carved on. This allows a cart to leave a slushy trail through snow when travelling slowly, and allows ships to melt their way out of ice ten feet at a time. This keeps the vehicle frost-free, but also has the effect of preventing you from carrying ice or frozen goods for transport, as they will thaw out.
Day 14 rune script:
I, (the runemaster), guard this ship in winter - Isa(Raido) General, Method II - gives a bonus equal to the magnitude of the rune script to the ship or cart the runes are carved on. This bonus applies to winter travel, avoiding slipping in icy conditions, exposure damage.
(The sample Isa scripts in the book are used for affecting people or animals, but using Raido as a secondary rune means you can help ships or carts in the ice and snow).
While I believe that you're right. Is there some way to harness the natural (i.e. in some cases, non-magic resistance triggering) nature of rune magic to avoid this?
When rune magic creates things, those things don't trigger as inherently magical, they slip right through magic resistance. Could a Rune magie somehow set up an age slowing effect as a natural thing not requiring a continuous effect? I guess it would have to be creation of non-magical age slowing substances similar to theriacs from Art and Academe.
Can rune magic be used to modify the Living Conditions modifier instead of the Aging Roll itself, possibly shifting any Warping to the environment (which if in a low level Magical Aura, may not itself be subject to Warping due to its magical nature and not cause Warping due to its strength?)?
HMRE p125 "Rune magic still causes Warping to a target over time, even though its effects seem natural, as a consequence of being exposed to a constant magical effect. The target also experiences Warping from rune spells of Level 30 or greater, unless the vitki casts the effect on himself."
The Dagaz guideline is "The target received a bonus or penalty to Aging rolls equal to the magnitude of the effect, so long as the rune lasts for the entire year". As it mentions Aging rolls directly rather than living conditions, no.
This does raise the question for Learned Magicians, does an amulet to raise Living Conditions with a target of Structure or Boundary cause Warping to the environment instead of the inhabitants? I think no, but there may be an argument otherwise.