Just playing with ideas regarding initiation scripts and the Corruption of House Tytalus. I haven't dealt with Initiation Scripts before.
Perhaps one of the demon dealing Tytalus had managed to avoid losing his soul for a long time while getting mostly untainted magical secrets in return. Say initiation scripts for Hermetic virtues and/or some of the virtues from HMRE.
And said Tytalus after finally becoming damned, decided to write these initiation scripts down for others to find. Perhaps the Quests to find each script count towards Initiation.
With perhaps one of the scripts leading to infernal damnation, while the others simply inflict the Flaw "Tainted with Evil" - perhaps as an Ordeal, perhaps as a side effect of fulfilling a Quest.
Does the above make sense? I haven't checked the numbers yet.
Nothing you have posted really needs to be checked by numbers and it all makes sense. You could use many of the demon related flaws as an Ordeal. I would suggest looking through RoP:tI if you really want to dig up some demon related Virtues and Flaws.
The only thing I would caution is to make sure your players have no problem with possibly getting the saga dragged into demon overloaded waters. Some do not like it for a variety of reasons, including having lived through 3rd edition.
I'm pretty sure this made it to the published line, or if not certainly Sub Rosa...
I added effects to reading certain books. For instance, a complex and confusing book may eat into the ten days of allowable time a magus can spend in a season before it impacts their study total. A frustrating book may lend the character a "Frustrated" personality trait as they try to wrap their head around the content and continually fail.
It's one of the things I like to do, to bring additional qualities to things that the characters interact with. So go ahead, add those traits and qualities and provide some kind of consequence to using certain resources. My yardstick is that these things are temporary/transient and don't fundamentally change a character in a way that the player does not embrace.
Suggesting that the magus spends the season being frustrated and grumpy and is a trial to be around while they read a volume is one thing, and at the other end of the spectrum is leading the characters to commit actions they might otherwise not undertake.
It does make sense. And I do believe that there should be a lot of such tainted scripts around. Some may be transparent, making it clear that the mystery is infernal. Others may be demonic deceptions. Yet others, as you suggest, may have incidendental infernal side effects, from the quest or otherwise.
The challenge, I think, is to play the corruption and damnation to make a good story, maintaining the free will of player and character alike. The demon cannot just inflict damnation. It is the character who willingly give up their soul in exchange for something else.
I would not be so worried about tricking the characters into an infernal turn which the player does not want, but I would give them a chance to turn back, possibly by preparing a pilgrim story. Tricking the story into a dark theme which the players do not want would bother me more.