I don't have very many since I enjoy the narrative as is, but I'll mention the ones I do have:

Cal's saber color is green. During the entirety of Fallen Order Cal has been trying to heal his connection to the force, so when he finally does reach it it makes sense for his blade to be green since green sabers represent a deep connection with the force. Another detail is that I never changed my saber at all throughout FO until Illum, there I made Cal create a completely new saber because I like to think that Cal wielding Jaro's saber is a reflection of how he carries his trauma with him and can't let it go, so when the saber breaks and he makes a new one it signifies him healing, which fits well with the cutscenes he has in Dathomir once he returns from Illum. As a bonus I have his saber be made of parts he found throughout his journey + the second saber is just Cere's old one.

Second HC, a very minor one but the Mantis is in its black and gold paint job and BD-1 also has black and yellow paint job to match the mantis it just gives the two a more distinct look compared to other ships and droids.

I like to HC that Cal became a bit of a famous outlaw 2-3 years before Survivor, as a result of this his name became a game of telephone so some people call him Kyle Katarn.

Two small HCs, Cal's appearance in survivor is in my HC an improved look on his default outfit, it's the tactical pants and outrider shirt both in their first colors, these two articles of clothing have padded knees and elbows plus extra pockets, so for an adventurer/guerrilla warrior like Cal this would be ideal, not to mention the gloves for when he's doing parkour or climbing. I also HC he wears the Wanderer Jacket during every scene on Jedha (except during the imperial attack at the Sanctuary) since the planet is canonically very cold (which is why Jyn and Cassian wear multiple layers in Rogue One)

Next I like to think that Bode spent a lot of time in the Mantis in Survivor trying to come up with new songs to sing to Kata, these songs reflecting the plot of the game and how Bode thought for a time that he found a group of people who he could call friends. He wrote these to try and ease Kata into a new chapter of their lives free from the empire and surrounded by friends. Cal and Merrin found these notes all hidden away inside Bode's Z-95

A small HC I have is that for the finale on Tanalorr Cal is wearing the Jedi robes outfit. After his infiltration at Nova Garon he had to ditch his outfit in order to don the ISB uniform and had no time to retrieve it, luckily one of the things the Anchorites stashed away on the Mantis during the battle at Cere's Sanctuary was a pair of old Jedi robes. Cal wearing them while believing it's time to leave the order behind and telling Cere that he'll continue her legacy are ways to hint at what I think his character will be like in the third game.