The thing that you want to achieve can only be done with the official inGame editor from SI (unfortunatly) and that is the only reason why I use both editors.
When you change the CA of a player the game itself alters the attributes (sometimes nearly immediatly sometimes it takes a week or so) so that they match the new CA
When you change the attributes of a player and DON'T change the CA then the game will alter the attributes back so that they match hte CA after you did your changes.
Only the inGame editor (witch is not yet available in BETA) shows you the new CA (that will be needed after the attribute changes) when you change the players attributes.
I think this is a feature that FMRTE can't implement because SI NEVER (in all the 20 years that I play FM now) answers questions about the calculation of the CA
There are some basics known though.
A player attribute counts differently into CA depending on his position for example
Some important attributes do not count into CA at all (all attributes that define the players personality)
Those calcualtions are very complex and it becomes even worse when a player has several positions
Being left footed counts heavier on CA than being right footed.
Being both footed counts heavily on CA (it's about 10 CA points which is really much when a player only has a CA of 80)
Being able to play serveral positions counts on CA (reduces points available for attributes) but some combinations of positions help to reduce the points certain attributes count on CA
etc.
Oh and when talking about player development...
There are soft caps when it comes to the possible CA of players reguarding the league they play in.
A high potential (above 120) young player in English League One will never reach his full potential when he stays in League One (this is one thing that you also can see in interviews when you as a manager have the option to say that you think the player will 'outgrow' the club)
Rule of thumb for English leagues is about:
120+ Premier League
105-120 Championship
90-105 League One
75-90 League Two
60-75 Vanarama National
45-60 Vanarama National N/S
Around 160+ is a CA für National Team players in the bigger countries