Will KIP-0010 break existing Kaspa scripts when it activates?

No — existing Kaspa scripts are explicitly designed to continue working after KIP-0010 activates. The activation is purely additive: before the DAA score threshold, the new opcodes are treated as invalid (leaving old scripts completely unaffected), and after activation the new capabilities switch on without altering how any previously valid script behaves. This matters because it means Kaspa can expand what its scripting layer can do without forcing developers or users to rewrite or redeploy anything that already works.