The test cases in a given test plan should be sufficiently similar and should not have wildly divergent paths depending on the value of parameters in a test case.
When you do find your test case flow diverges too much you often want to either break your test plan down into a few different test plans, so that you have a plan for each different kind of pass through the system.
Another similar approach is that you may want to decrease the scope of your test plan a bit so that you end up with test cases that are all similar in the plan.
Lastly, let's say the flows aren't wildly divergent, but only slightly so. As a silly example let's say you were testing a recipe that varied based on the fruit selected.
Fruit: Apple, Grape, Orange, Banana
And then you wanted a step for how the peeling was done.
Peeling: By hand, By manual peeling tool, By automated peeler Peeler type: Hand crank, Battery powered, AC powered
Now... our testing flow here has some divergence. Grapes and Apples don't get peeled in this recipe, so they never enter that flow. And Bananas are always peeled by hand so they only get a part of that flow. If this was just the tip of the iceberg of the divergence, we should create a test plan for Grapes and Apples and a different one for Oranges and Bananas.
But if this is the entire extent of the divergent flow, then we want to take advantage of N/A values and married and invalid pairs.
We update our parameter values for the peeling flow to include N/A.
Peeling: By hand, By manual peeling tool, By automated peeler, N/A Peeler type: Hand crank, Battery powered, AC powered, N/A
We marry Grape and Orange (uni-directionally) to the two N/A's so they don't participate in the peeling flow. We marry Banana (unidirectionally) to "By hand" and the 2nd N/A so it has a partial and circumscribed pass through the peeling flow.
Lastly we don't allow Orange to be paired with either N/A with an invalid pair.
That's how a slight flow variation can be accommodated. Please comment with any questions about any of these approaches to your problem.