For your 1st case, you can use either SegmentContent by your 256 bytes (or perhaps you can even use SplitText) https://nifi.apache.org/docs/nifi-docs/components/org.apache.nifi.processors.standard.SegmentContent/index.html https://nifi.apache.org/docs/nifi-docs/components/org.apache.nifi.processors.standard.SplitText/index.html
For your 2nd case, you can use ReplaceText https://nifi.apache.org/docs/nifi-docs/components/org.apache.nifi.processors.standard.ReplaceText/index.html Thad +ThadGuidry <https://www.google.com/+ThadGuidry>
