Clarification on Error Propagation

#1
I thought I understood the basic operations for error propagation (addition, multiplication, etc), but I have a few questions:

1. Is variance the only measure you can use? I only have 95% CI available to me.

2. Does multiplying/dividing a mean +/- CI by a constant preserve the error (ie CI value)?

Example: converting mean weight (kg) +/- CI to mean weight (lb) +/- CI?

Thank you for your assistance. I'm not sure what the proper way to propagate my error is or to find a new CI after these operations.