Come to think of it, Morrigan hasn't changed at all.

Could it be that any apparent change in attitude is down to Morrigan learning from her time at the Orlesian Court to be more guarded about expressing her opinion when it might not be in her interests to do so. When we meet her in DAO she has very little experience of the wider world and so has no reservations about saying exactly what she thinks. By the time we meet her in DAI she has observed the Game and has realised that sometimes you need to be a bit more subtle and less open when dealing with people in positions of power.

I do not recall the exchange with Cullen at all but you are right that her attitude with Solas is more typical of the Morrigan we knew before and that is exactly because she does not regard him as someone she needs to worry about upsetting as she wants nothing from him. By contrast, the Inquisitor is someone that she does wish to cultivate and so she is more polite as a result.

Ten years have passed from when we last saw Morrigan and she is older and more experienced than she was then. It would be surprising if she hadn't learned from her greater exposure to other people and modified her behaviour as a result.  She is clever and observant but that doesn't mean her underlying character is any different to what it was before.