The main immediately noticeable change in behavior is that he has become indifferent.

He also rarely shows sense of humor and rarely jokes.

Might be sassy.

Might be really brutal, but that usually only in last resort.

Other notices:

he still likes coats

style is still quite formal, but now have more steampunk vibe

clothes colors are most often gray and black

he wear bracelet still, but now under his glove

gloves and waistcoat can be optional

claw scars on arms

• Same like in original concept, he really dislike his scars. 
• He often avoids mirrors, rivers or other lakes because he doesn't want to see his reflection. He hates how he looks because of the scars.
• Platinum broke his tail. Now Alojzy has no feeling from the point of fracture to the end of the tail. 
• Scars on arms and bitten off ear he have also because of Platinum.
• He still hopes that his Jasper will come back one day. 
• He evince a slight Stockholm syndrome.
• Despite the brutal training he underwent with the Traders, he didn't lose his goodness and sense of justice. Anyway he is forced to do everything what Traders wants. And he do it. If he hadn't, there would have been quite painful consequences.
• Every time he had to kidnap someone, he felt terrible remorse. And especially when it comes to children. He always remembered himself him from the past when he himself had been kidnapped and how terrible it had been for him.
• He's not in very good mental condition. Among other things, by the contrast between his worldview and what he is forced to do. The fact that he lost his Jasper doesn't help either.
• His face almost always shows indifference. Alternatively anger but that not often. The only exception is when Jasper appears nearby. Then you can see fear or an apologetic smile on his face. 
• At the age of about 30, he will go crazy with unrequited love.