@tonewolf
I'm fairly certain you can't kill real events, you have to make them artificial. For your use-case I think it's just a matter of making the note artificial in the onNoteOn callback and storing the ID. Then you can control it how you want in the note off callback.
Here's an example
HiseSnippet 932.3oc4W8zaaaCEmJ1pn1cqXsqnXG0gcvAHqvZqqs.EEMIN1EFqNwHJMa2JXod1lHTjZTTdyXXe21Gg8QoG18sGkThjVTybL5Vw1zAC+9G46u+dRS0JFjjnzDmNmrJFHNejavJoYwfETtjL9.hyscmPSLf1Km09qhoIIPHwwo0KrLb5zlj871muOUPkLnjEgbphyfWxi3lRtS28a3BwHZHbBOph1Ob2wLkbfRnRQ+okaeRLkcFcNbH0p1VtDmaLLjaT5.C0.InN6qBWErP8Cxb8Okmvei.rD9j.7fxYSFrfKBmddrlPHNtSKi7V4Q98bmvC4WvuLC7IYB7JsnZNvYqqxk7uFtjSEWpctKcG2.llGaJkX8ma4NVhEjYTLUW0Ux0k37KtCTnBRyChnmAizHwEFz6Q86uiG9y1OcVpjY3JomRdnx.GI6sc2epamt+bWu+rnYyZTl8ZzJg.zMJ1Vc0Wkg8joQuAz63sjJRgKTDC+54zard4TVdTWQQkbrjaNJFJnGoDg1bk8+WtBPJRa3+d03CnFpsnTvC0KFzFt0cbN.Vhc04knNtG.ImYTwXe8kpeXmiJLUPM0amryMEBv7QsZnsPIS3lUUmqtF8X8uxdr00Eui6TtgsnYebqF7QLS82gOVLY9wtCmMCXlRGrs6nuaSGCW+q+14W+sbC3RHCVL6xueFs22RWBdu.jf1l77uBjweccQFiWajwiXF75OQSkIwpjZGb.DwOQIsYgRluJAABfu+Xa0rJ+AJptQQu84ivfrQaBnlTcVawdQpTooVaPq50g1q2na8IhJ52.NY6O.P28eOAc+oEbK8H+Fgv+MWML2CVhHOiCeWH0Eh8dl2D7nv8jY386gnTy3LNUza6m9tAy6zsSVG8CnggmpDoQfssqWwYtimee6hhuv2to3CDru66KX++OB0Wqmry49X.OJV.CkKAAFjY93cwnZFMUXNma8NxIJoJdgRxYUGyOFLZ974ftpu2X.smwfuDWIm6s6wf.nUgr97ceIB0P0XdB1vbw0+UqZrd8Yt4tqmsG16euqna8e6UzGqRMb47ITrI7GQbhCSiBvMiL.ucoDDVrCmsrS44z8sz4qFkgYD+N9THz2R6THz+bg+ibGQTlV8ZVNpnsO8lYbv3Vl8EOcvO8Bo87IYHkUqkQ3ZsWyX0OpKY3WtoF9UapgObSM7q2TCezlZ3i2TCexesg125XuTiJJezjPlLcX1ZFGmgRJ1kmMQP9C3+t.QK