Is it possible to undo the changes of DA regarding espionage?
Not specifically, though you can easily mod all improvements to be immune to sabotage, thus rendering spies completely impotent.
How accessable is the mining system to modding?
It appears that the values involved can be changed, but the fact that those values will only affect manufacturing seems to be hardcoded. Depending on how it is handled in the code you may be able to add additional upgrades to the existing path, but other than that options look limited.
- What can I do about the new treaties? Due to the weight put on them regarding the price-tag I sense that they are similarly disruptive to the gameplay as super-abilities and super-events and I will very propably desire to tune them down a lot both in terms of price and gain as in terms of influence on the AI's decision making.
Treaties give the race you give them to a bonus equal to 10% of your economy or research (you don't lose that 10% yourself). However the AI won't give them unless you have *very* good relations, and they can only be given to one race (and only revoked by war or death). Treaties are not really moddable.
Does the Ai still use the basically same structure to decide what to
research and how to equip it's ships or has this section recieved a
complete rewrite?
Frogboy did a significant amount of work on the AI's research priorities
after the public beta ended.
Is it possible that we can't modify the "Buy now"-feature at all?
Aside from the names of the companies, I don't believe you can.