Being flexible in your strategy is more of a matter for you to figure out in many ways. Your book will have specific strengths and weaknesses for different strategies, some you don't even realize are there. The best way to extend your strategies is to always be looking for the best thing you can do in any given turn, and to look at your book to see what you wish you had done on any given turn. When those don't match, keep an eye out for that set of circumstances in the future and go with the plan you wish you had used. If it works for you, you have a new strategy.
I had similar issues with my necromancer at first. It's built to run 2 spawnpoints, two crystals, two harmonizes, and a ring for maximum returns. Most everyone on here will tell you 3.5 turns of mana harvesting is a bad idea. So I worked on a number of different openings and trying different tactics. I can run much leaner and meaner with one spawn point, or open with two but time the use of spells so that I'm pumping zombies out starting from turn 2.
The point is, you can always make what you have work differently, and you can always figure out what doesn't work and replace it.