The following are house rules that apply to the Aestas setting. They are in no particular order.
Armor Encumbrance
The weight of armor is spread more evenly than something carried in a pack. Add only 1/2 the total weight of worn armor when determining a character's encumbrance.
Magic and Spells
The Salamander Curse is the primary obstacle to using gunpowder. On any roll of 18 while using chemical explosives, 1d small fire elementals will manifest and attempt to consume (explosively) any gunpowder or other chemical fuels in the immediate area. They will linger for 1d minutes or until they are slain, banished, or otherwise driven away. Larger supplies of gunpowder, or concurrent explosions will attract more fire elementals, potentially leading to disastrous chain reactions.
Lead can be used to block magic. A significant thickness of lead will hinder any magical effect that has to pass through it, such as a room with lead paneled walls. The seal need not be 100% air tight, merely substantial - even a 1/4" thick sheet of lead (which weighs about 60lbs/square foot) will block magical effects, except on a Critical Success. This does not apply to direct effects like blasting spells, physically manifested spirits, and so forth. It primarily effects Scrying and Teleporting spells, allowing a measure of privacy where needed.
Create "_________" spells are not permanent. Objects and materials created will generally last no more than a day at most, ultimately vanishing in a flash of harmless but startling light and sound as they lose coherence and disappear. Any mage will be able to recognize magically create materials upon inspection with an IQ+Magery roll.
The Unofficial GURPS Magic Errata all apply to Aestas. Assume that the most restrictive readings of the "Economics and Standard Magic" apply to Aestas, to minimize the world-altering impact of some very common spells.
Since GURPS characters tend to get into dangerous situations where people are trying to harm them, the characters' careers could easily be cut short unless a lot of GM intervention is involved. Using GURPS xp to modify die rolls allows characters to have a bit more control over their characters, and emphasizes that combat can cost them. If you use these rules, you should probably increase the amount of xp you give for an average session of gaming by about 1 or 2 points, on average. Players should save some of their xp in case they need it, since if they are all out, they must rely on the luck of the dice. Here is how to spend xp:
Make a critical failure a normal failure.
Reduce damage taken after DR by half(50%).
Automatically make a HT roll.
Modify any die roll after the fact by + or - 3.
Characters may also opt to place some or all of their xp into a team pool. This must be done at the start of a session (yes, this is borrowed from Shadowrun) or a campaign. In order to use xp from the team pool, all team members present must agree to its use. The team pool can be redistributed at any time, with an equal number of points being given back to all members of the team.