I have a good 30 titans of different types in my Chaos army, and I'm making my way through them all and giving them different conversions and mutations to make them as individual as possible. And this made me think, whether Chaos, Imperial, Ork or whatever, no two titans would be the same, especially over time and battle experience.
I was never able to read into depth the original Adeptus Titanicus rules regarding titans, but I knew there was a little bit of degree in personalising them. Obviously it's tricky, and I'm not suggesting free reign, otherwise we'd have people having a Warlord titan with 10 guns that can fly! But I'm hoping to get ideas together to introduce some level of advantage/disadvantage adjustments going so that the titans can stay the same points value but each has their own quirks.

For example:
I've got a Chaos Reaver titan of Nurgle that pretty much vomits everywhere. It does have an extra attack from the head, same as the Great Unclean Ones stream of corruption template. Only it has to fire it every turn regardless if friend or foe is in the firing path. Also if given charge orders, it staggers about, much like some drunk about to relocate the contents of his stomach. So it may well walk into a building, or trample friendly troops.

Customizing Chaos titans is an easy thing, from a modelling point of view it practically calls for it. But other races can do the same thing. Gargants would never be built to be the same so they could have things like being able to move faster but having less armour on the lower regions to allow for freedom of movement of the legs. Imperial titans would gain their own quirks over time as they fight different foe and have repairs/upgrades carried out.

I'm planning on posting more about my titans as I do them to give you guys ideas. Some of them are definitely out there!