In my understanding, a spinoff should work exactly the same
as the original, so altering the difficulty adjustment would
just make it an "independent" altcoin.
The idea expressed by Peter R in the original post of this thread only talks about making the initial distribution in proportion to a snapshot of the Bitcoin block chain:
Since the market has already encoded its best estimate of the most efficient distribution into the unforgeable global ledger known as the blockchain, why not use this? Since all bitcoin users can cryptographically prove ownership of their share of bitcoins, the code-base of any alt-coin can be modified in a trivial way to allow bitcoin users to claim a share of any pre-mine in direct proportion to the percentage of bitcoins market cap they control. This method (a) bootstraps alt-coins with a very large potential user base, (b) places all alt-coins on equal footings thereby allowing them to compete on their own merits, (c) automatically piggybacks bitcoin investors in any financial gains that may result due to community innovation, (d) fairly rewards innovative alt-coin developers as they can scoop up spin-offs dumped cheaply on the open market, (e) makes it difficult to pump and dump.
Later in the thread someone referred to alt-coins that do this as "spin-offs."
I have not read anyone suggest other requirements than the initial distribution for an alt-coin to qualify as a "spin-off."