Pink Dot Rule: Without getting into too much 'why?', I think I'm fine with the idea that (if resisted), Parma will stop the magical effect but not the physical sword (assuming the sword was completely mundane).
I'm listing a few House Rules used from my Saga that may be of interest:
Vis may be "coloured" or "flavoured" in addition to, or in place of, standard Arts. For example, what appears to be a pawn of Mentem vis, may function as 3 pawns of vis for the purpose of summoning spirits. Alternatively, it may be a 3 pawn vis source only for summoning spirits, and not work for Frosty Breath of the Spoken Lie. This keeps the mystery in magic.
As with Flavoured Vis, Auras may be aspected to work better, worse, or only for a very specific use. Auras may carry multiple such modifiers. For example: A magical aura in a swamp may rate as Level 2, but add +4 to disease-type spells. A level 1 magical aura near a volcano may add +6 to fire-type spells, but penalize Aquam spells by -6.
Spontaneous Spells and Form & Effect Bonuses
In keeping with the Focus & Effect (F&E) charts printed in the ArM5 main book or any subsequent books, a magus may use items to add a sympathy bonus to spontaneously casted spells, to help them achieve more powerful effects. For example, while casting a spontaneous spell to make oneself invisible, using a quartz will add up to +5 to the spell casting roll (before division). These F&E bonuses are capped by the magus' Magic Theory. (This is something from older editions of Ars Magica, and I like the idea of trying to boost a spell by getting a sympathetic item. Makes it seem more... magic-y.)
A magus may attune an invested device as his talisman in the same season as its creation (or in the last season of creation, for multiple-season projects) without any additional costs. An existing device may be opened for attunement and 2 casting bonuses in a single season.
A player may change the specialization of a given skill when enough experience points have been accumulated to increase the skill. This change also has a roleplaying requirement to justify the change.
Language Exposure Rules
Characters can pick up a new type of language exposure experience that stacks regular exposure experience to represent picking up the local language. Characters can pick up a maximum of 1 xp per season in a language spoken by the locals of their area. If there is more than one local language, the character can pick which one to gain the xp in. You cannot learn to speak better than the prevailing average of the area. Unless otherwise indicated, a character may only earn enough experience to gain level 4 in a language.
This language exposure experience is limited by personality traits like xenophobic, proud, prejudice, reclusive, or any other trait that would preclude the character from wanting to pick up another language. For every point in these personality traits, one season of this language exposure experience is lost, starting with the Spring season. It is possible, with enough negative personality traits, to not gain any local language experience.
e.g. A character living in England without any negative personality traits would gain 4 xp in Middle English, at 1 xp per season. The same character with Reclusive +3 would only gain 1 xp in Middle English per year in the Winter season.
Area Exposure Rules
Every year (in the Winter season, but not for the first Winter season), each character earns 2 xp that must be spent (Local) Area Lore, until a score of 2 (15 xp) is reached. This rule encourages some verisimilitude in that characters gain the Abilities to represent basic knowledge of their surroundings. The extra XP are free because forcing characters to invest XP in increasing Area Lore diminishes their already limited Ability lists.
Rules adapted from Atlas Games forum thread "You're what?" and a Durenmar essay, "Hermetic Babies" by Shannon Appel.
Determine Number of Children
Roll a stress die:
* 1: Possible "botch", roll 1 Botch die to confirm (more may be added if circumstances fit)
[*]0: Botch: Birth results in hermaphrodite, child with animal features, or other unusual features
2-9: Single birth.
10+: Possible "crit", resulting in multiple births
* 2-10: Single birth, see 2-9 above.
Determine Gender of Children
Roll a simple die for gender:
* If even, female
- Determine Gifted status
At the time of birth roll a stress die.
a 15+ the child has a Minor Supernatural Virtue.
On a 18+ the child has a Major Supernatural Virtue (or multiple Minor Supernatural Virtues)
On a 21+ the child has The Gift
+ the Aura modifier for the aura in which gestation occurred.
+2 for each parent with a Minor Supernatural Virtue
+4 for each parent with a Major Supernatural Virtue
+6 for each parent with The Gift
Note that Supernatural Virtues will be influenced by the Aura at the time of conception. Only the highest parental modifier applies; they do not stack for a given parent. (e.g. If a mother has both The Gift and Dowsing, she modifies the roll by +6, the highest of the parental modifiers.)