Does a diameter of a brake line affect braking pressure

According to Pascal's law, pressure must everywhere be equal. Pressure is defined as a force on a surface. Pressure equals force devided by area P = F / a. That is, the area of the master and slave cylinders (those inside the calipers or brake drums). So, brake pressure is only affected by the area of the master- and slave cylinders and the force that's applied to the brake pedal. This answers the question, but here is some more information:

Since P = F / a, F = P . a. If you have a master cylinder with a surface area of 10 cm^2, and you have a caliper with two 25cm^2 pistons, the total surface area in the caliper pistons is 5x greater, thus the force applied to the brake disk is multiplied by 5.

In practice, brake force is mulitplied even further because of mechanical advantage. The brake pedal (or brake lever on a motorcycle) provides leverage. Also vacuum powered brake boosters are used to create more pressure.