BI2 is a game I loved (I used to have the CD version) but never completed.

Now I remember why.

The music, controls, units and missions are all excellent. Unfortunately, some missions have a turn limit. But the game doesn't tell you in the briefing, and doesn't give you any visible indicator. You can play a mission for hours, then suddenly get a "Game over" message. You can't go back to a recent save as it is the same game, you won't have had enough turns left.

If GOG had added an option to remove turn limits the game would have been perfect, and highly recommended. With the turn limits it is just too frustrating.

I don't suppose there's an easy way to disable turn limits?

Doesn't the turn limit appear in the information screen?

Yes, it does. You can see the current turn and the limit turn number. I do not remember if the Game Over is at or after the turn limit number.
The first time critical scenario is the one where you are trapped and need to find the way to the airport in the south. You only have a convoy of units and no factories. Instead of overwhelming the partisans you need to march through the map along corridors in the jungle. It is just normal to lose on that map at first.

That's correct. But there is an easy way to change energy and material for each buildiung and to change 4 production slots of each building to fit your needs. It's called cheating but the AI is cheating sometimes too.

I did not fully decode the list of units, but with some limited amount of try and error you should be able to alter the type of unit or the owner.

The structure of each save game file:
The data for buildings can be found at position HEX 5840 (scenery disk HEX 5a70).
The data for units can be found at position HEX 19b0 (scenery disk HEX 1bdc).
At position HEX 58 and HEX 59 is your energy (blue player). At position HEX 60 and HEX 61 is the energy for the red player.
After changing any material or energy value, you need to enter the menu and watch the overall info panel of the game, e.g. turn limit, player alliances, number of units, etc. Otherwise the game is showing old values.

Please note that Battle Isle 2 is using a Low Byte High Byte encoding (little endian).