For more on editing scenarios, see this primer I put up: editing-scenarios-with-enhanced-t146.html
Campaign editing has its own problems; after all the scenario work is done, you have to re-load the scenarios into the campaign structure. You may also have to adjust the initial Buy Points, due to older OOBs having different unit costs. If the campaign was originally intended for, say, a tank company and an infantry platoon, all of which used to cost more in the older version, the player might now have enough points to buy 2 tank companies, which may unbalance the campaign.
The best way to deal with this is to check the intro text for the suggested force, then purchase those units and note how much they all cost (including the cost of the A0 unit). Buy the most expensive versions (the best tanks, the heaviest armed infantry, the largest caliber artillery) and add another 5-10% for flex; some players do not use the True Troop setting, or the Reduced Squads one, which will make for more expensive units. Now change the points in the Build column for the first scenario slot.
I wouldn't recommend messing with the other points unless you know the original campaign inside and out; the rebuilding and support points were often figured based on what the designer wished the player to have access to at different stages of the campaign. For example, in the Desert Rats campaign, we used certain scenarios to let the player completely rebuild his force with different tank units, to represent a move from the 11th Hussars with armoured cars to the 7th RTR with Matilda tanks. Without the large rebuilding points, the campaign will not work the way it was intended.