How to modify expression rule without break compatibility

Keyword or "label-value" is certainly preferable. Besides being more "change-proof", it also has better readability. You will need to type the parameter names and their values(and some may frown by saying that it takes a lot of typing), but the advantage is anyone who is reading the code later knows what parameter is taking what value.
Passing parameters by keyword makes it very explicit, reduces the chances of errors. Imagine passing parameters by position, and let's say some other developer removes a parameter. Any rules you created that are dependent on the rule which changed will cause errors in your rules also.
A point that you should keep in mind - Although passing parameters by keyword is a good practice and preferable, custom plugin functions do not support it. But expression rules created in Appian do support the keyword syntax.

Keyword or "label-value" is certainly preferable. Besides being more "change-proof", it also has better readability. You will need to type the parameter names and their values(and some may frown by saying that it takes a lot of typing), but the advantage is anyone who is reading the code later knows what parameter is taking what value.
Passing parameters by keyword makes it very explicit, reduces the chances of errors. Imagine passing parameters by position, and let's say some other developer removes a parameter. Any rules you created that are dependent on the rule which changed will cause errors in your rules also.
A point that you should keep in mind - Although passing parameters by keyword is a good practice and preferable, custom plugin functions do not support it. But expression rules created in Appian do support the keyword syntax.