Not sure if Teutonics Knight is required, an analogue to the German Empire might be sufficient; you know, have a dominant regional black-and-white flag be picked as the basis for the new Imperial flag. I'm not sure if one exists, though.
Of course, it'd help a bit if there was a contestant for the German imperial title, as in OTL but with the roles , which could maintain the old black-and-gold colours; don't forget that the OTL Austrian empire only got rid of black-and-gold because of the fusion with the Kingdom of Hungary.
So, it's not unlikely the Habsburg Empire would use non-Holy Roman Empire colours if the Prussian-based German Empire had already chosen to use them, but you'd need to find a source for that black-and-white. The Teutonic Order is a possibility, but unlikely considering its ties with Prussia. Of course, you could just always make a source up; this is AH.com, after all.
but just altering the flag wont affect the history i think ?
Depends on the exact circumstances of how it occurred, and why this one was chosen. A different flag by itself wouldn't necessarily change history to a significant amount, though.