How do you make curves on the surface without bolleana?

How do you make curves on the surface without bolleana?

Hello

I have a doubt with respect to curved objects,
How do you solve when you need to make these curves as the example of the picture,

I know that many people use the bolleana, or move the vertices, but would not have a tool like a scalpel but with the control so that they could draw directly on the surface?

Extruding an SVG or bezier will do what you're illustrating above. It may not work in more complex cases (e.g. carving a face into a pumpkin) but for a simple flat surface it's perfect.