"Apply for" vs. "apply to"

In this context,

Apply: to be pertinent or relevant; have a bearing on; concern

• A rule that applies to everyone.
• What I have said does not apply to you.

So, the correct answer is:

This function just applies to Conductors, RYSP and Officers.

"Apply to" is used when we are saying where something is relevant. e.g. "That rule doesn't apply to me." "Normal logic does not apply to political debates."

"Apply for" is used when we are requesting something. e.g. "I would like to apply for the job of senior sanitation engineer." "Jack applied for a credit card."

Apply to: This rule applies to everyone. Apply yourself to this task.

Apply for: To apply for a job