I am not sure I can completely follow what you are trying to accomplish with the profile. Are you ultimately trying to lock in the grade of the profile line and have it extend to the intersection point? If you are using the Profile Line Between Points, it will establish the start and end points and the manipulators on the line will be for the length and slope. Can you pick up the arrow on the length manipulator and adjust the end of the line until it intersects with the profile gradeline or gets to a station you desire?
Or if you are using another tool to establish a base vertical you can use that as a template for creating a new profile using the Vertical Geometry tools.
Or if you are using another tool to establish a base vertical you can use that as a template for creating a new profile using the Vertical Geometry tools.