Yes, but presumably the writers knew of Asha's existence prior to writing the first season, and knew that Asha was going to be significantly more prominent than Osha. Would've made more sense to call her something else had they been planning ahead...
The idea to rename her clearly occurred fairly late in the game. I think earlier in this thread there was a casting call which still identified her as 'Asha Greyjoy.'
The showrunners aren't capable of prognostication. It's possible, you know, that it never occured
to them that the similarity between Asha and Osha would be best avoided by naming the characters differently until they were casting Asha for season two. The only other major character's name they've changed so far is Robert Arryn (to Robin) and since he actually had the exact same name as the King the issue was a little more obivous. They probably figured on calling her Asha when they were filming the first season.
That happens, it's television, not every difficulty or issue is going to be foreseen.
As for Alton Lannister/Cleos Frey, I have no idea why the rename, particularly from Cleos to Alton. Of course, there are so many Freys to keep straight anyway.
Oh the change to a Lannister makes sense. The thing that actually matters about Cleos Frey is that he's related to the Lannisters and is thus a prisoner of the Starks. That he's also a Frey - the family that is currently allied to the Starks - is a bit of a wrinkle that'd take at least a scene to explain and not a detail we particularly need.
But from Cleos to Alton's the bit that throws me.