Suppose that I want to send a very large chunk of data using IP, and that the data gets fragmented into 100 IP datagrams.
By the time I have sent the first 90 datagrams, I realise that I would like to tweak a few bits in the payload of the 3rd datagram. Is it possible to send an "amendment" to the 3rd datagram before sending the last 10 datagrams, avoiding me a resend of the initial 90 datagrams?
Part of the reason I ask is that this RCF says (see page 1):
[a new fragment] may overlap with existing fragments
This absolutely can happen in practice but it's often part of an attack or detection evasion technique. I've not heard of anyone using it to correct previously sent data as you suggest, though it may be possible.
Here's a specific attack that I've come across http://www.slideshare.net/michelemanzotti/attacking-ipv6-implementation-using-fragmentation
and here's wiki on the technique: https://en.wikipedia.org/wiki/IP_fragmentation_attacks
This is the manual page in the Snort IDS about the preprocessor frag3 that looks for frag attacks: http://manual.snort.org/node17.html#SECTION00321000000000000000