Define Parameter on Fusion Composite

I'm creating a Fusion composite which requires a constant to calculates its parameters with expressions. The constant is used in several places so hard-coding it would make it harder to maintain and reuse.

Can you create your own parameter for a Fusion composite?

Is it safe to assume that you cannot add a parameter to a Fusion composite for users?

Add any node with needed parameter type knob to your comp and use this knob value in your expressions.

Add any node with needed parameter type knob to your comp and use this knob value in your expressions.

Thanks!