About replacing the handle: What kind of change are you planning on doing? Do you want to modify the current handle? (Eg make it thicker by adding thin veneers on each side?) Use a handle from another blade? Make one from scratch?
If you are in this for the results, not the process, and you have a small budget for this - esp if the blade is expensive - it might be worth considering getting an experienced blade maker to make an install a handle for you. (I’m told Charlie - bladesbycharlie - does this, and his fees should be reasonable. (His full blades start at $55 (USD), including custom handle...) I’m sure some craftsmen based on Europe can do this as well.)
If you are in this for the process, these things are often more challenging than they seem (if you have high standards), but they are also usually way more fun than we expect..