Hello Alan,
you ask a not easy to answer question, special regarding the influence of the Islam upon the the Javanese cultural perception of the keris since I know not enough about the Javanese cultural perception of the keris before Islam coming to Java.
But frankly said I think that this influence wasn't so great like others maybe think. By my first visit on Java 1992 I was surprised, special in Central and East Java, about the very own interpretation of Islam on Java. This changed in the time until now but I think that this can be neglect regarding your question. The outer appearance of the keris may have changed by Islamic influence but nothing else. I may be completley wrong so I would like to read your own opinion about this.
The colonial influence was much greater IMHO since middle of last century the "keris culture" was nearly moribund. This was prevent again by outside influence by only a few persons like yourself and Dietrich Drescher who has had a great effect that the keris forging don't died. Again, I could be completely wrong by my statement and would like to read your own opinion about this.
Regards,
Detlef