...I really don't think so. The dwarfen mindset is that you do not make anything unless you are 100% certain of it no its ands or buts. Him "improving" it after the fact would be the equivalent of acknowledging he gave a subpar product in the first place--since improvements are an implicit acknowledgement that the original product was lacking. The context of this gift was Kragg using his gathered 1000+ years of knowledge to create an artifact to repay a debt. In that light giving something subpar (which is how they'd view "can be improved afterwards") for the sake of quickly fibbing off, or cheating a debt, is like automatic Slayerdom Do Not Pass go territory.
He explicitly said that our sword was a rushed job.
Deep in the heart of Karag Lhune, Kragg grimaced at the Rune he had just struck. A shoddy job, it would barely last a century or two before beginning to fade. He resisted the urge to throw it back into the crucible; this was only needed for a single task, and in these dire times such shortcomings had to be accepted.
So it seems like he would be willing to acknowledge the problems with our sword, and he would be willing to work on improving it.