I metallurgical theory, you should be able to do it. I practice, I don't know. I'd be inclined to have the spring re-heat treated after the welding. Again, in theory, taking the spring to hardening temperature will cause it to pass through annealing temperature, where it will forget about all past stress. If you were going to re-heat treat, you might want to make the nib from the same material as the base spring, say 1095 plain carbon steel.

I hope some of the welders will jump in on this.