OK, here's some of what I have adapted.
Essentially, for lack of a better way to do it, I made Lightbearer a skill that a magically active person could take, assuming they were initiated in to the Lightbearers. Otherwise, you would have to handle it as adept powers, which would take an incredible amount of karma to get anywhere with.
I'd also considered simply making each rank a metamagic, then having the dice rolled for it be the initiate grade. That one doesn't require breakign the systems rules. It does require a lot more karma however. I wanted something that seemed more likely to obtain. Although this was written up before the SR4 Street Magic rule came out where you could buy a metamagic for 15 karma. So that may be a better way to adapt it. I'll leave that up to you. This is the system I used when I ran the character in question.
Now, I generally ignore skill caps anyway, so going above 6 isn't an issue for this. If you want to use them, well you'll have to use some other mecahnic. For myself, once it goes above six, you just add another multiplier to raise the skill (so a skill of 8 is 24 karma , 8*3).
Please, let me know what you think. The sytem isn't perfect, but it was fun.
[ Spoiler ]
Skill Ranks:
Rank 1 - Light Symbol and Shimmer
Really basic stuff, no real rule needed for these besides penetrating a glimmer. Disguise test is the same as the disguise skill, except you substitute the LightBearer Skill for Disguise.
Rank 2 - Light Sprite
Summons a variant of a watcher spirit. Not a toughy.
Rank 3 - Radiant Circle
Horrors or horror marked must over come Lightbearer skill + Willpower using Counterspelling + willpower, since they use Spellcasting in ED
Rank 4 - Heal Believer
This one I've debated on which attribute to use, but I settled on using Lightbearer skill Rank + Willpower. The other option I'd considered was Magic instead of Will. Same rules apply as per the heal spell. This one isn't as special in SR as it is in ED, do to the larger variations and effectiveness of healing magic.
Rank 5 - Karma Transfer
Never really came up, as there weren't a lot of other Lightbearers to recieve it. But the effect was to transfer Edge for one time use. So if someone were to recieve the karma transfer from another Lightbearer, they would get that persons edge . Ex: LB dies, has edge of 3. Another LB receives it. He now has 3 extra points of edge to use. Once these edge are used however, they are gone for good.
Rank 6 -Ease Wounds
Modified this a bit. Instead of having to make a test for all or nothing, I made this one effectively the same as the Pain Resistance Spell, where the force is equal to the Light bearer Skill Rank.
Rank 7 -Edge of Light
This one I debated a bit , but settled on adding the Lighbearer Rank to the DV of any melee weapon. It's strong, but it's supposed to be. That is only on horrors of course. Anything else, standard +3DV. I considered putting in something with AP, but that didn't really seem to go with the theme for me.
Rank 8 - Refuse Horror
Adds Lightbearer Rank to tests to avoid horror effects such as Fear, Control, etc. Similar to the Iron Will adept power.
Rank 9 -Lesser Incarnation
Now this one is strong, but that was the point of it in ED. And I figured that anyone buidling a skill to rank 9 had invested quite a lot of karma, and should get the full effect.
As with the ED version, they gain as many ranks to add to existing skills as the deceased/transfering adept had in the LightBearer skll. That's a lot. It's also limited to the max skill rank that the adept that died/transferred ahd the skill in, just as in the ED companion, which limits it a lot . If they don't have the skill, you can't raise it. Anything extra is lost.
Rank 10 - Avoid Horror Magic
As with Refuse Horror, adds the Lightbearer rank to counterspelling or spell resistance tests vs horrors.
Rank 11 - Armor of Light
Each Rank in Lightbearer temporarily becomes a point added to the adept powers Mystic Armor and Spell Resistance. This is one I hadn't really set my mind on yet. I'd debated using the same magic -weary component in Infusion. I'd also considered simply applying 1 box of stun damage for each round it is in use.
A straight Drain mechanic, I hadn't set on a value for it. In ED, the strain is 1 point per round, which is not very much. I'd settled on using the same as attribute boost for the time being, having them resist a box for each point of mystic armor they gained. But I'm not really satisfied with that one.
Rank 12 - Heal Any
Same as Heal believer, but applied to other people. Wow. Good if you're an adept and not a mage certainly though.
Rank 13 -Karma Increase
Another one I was concerned about , but decided to just go with, as spending enough karma to raise a skill to Rank 13 was quite an investment.
Essentially, at Rank 13, 14 , and 15, the Light bearer adds one point of edge to their total. Treat it like the Improved Physical Attribute adept power, just on edge.
In ED, they get a 3 point increase at Rank 13. I acutally tried this, and suprise suprise, it was too much. 3 is a lot, but over 3 ranks, not over powering IMO.
Rank 14 - Greater Incarnation
Same Manner as Lesser Incarnation, except it's 28 rank points. Again, any points they can't allocate (because they wold go above the transferers skill ranks) are simply lost. Also, they have to become a lightbearer within 3 months, just as with Lesser incarnation. that's pretty limiting as other Light bearers don't really exist, unless you want to get Harlequin and Ehran together to initiate you.
Rank 15 - Astral Shift
Treated as the Astral Gateway power at the moment. You can fully enter the astral plane ,go somewhere else in the world, and come back. Yeah for you.