I tried doing a search, which came up with literally nothing, and I did read the readme on the thread for DFHack and still have some questions. I'm playing around with it a bit on the arena.
1. What does the flow bits only function do?
Be advised that I have not used this tool; I am only looking at the source code, which I have not studied in detail. Anything I say here may be totally wrong.
It looks like "flow bits only" makes dfliquid
not place new water or magma on the map. It makes it only affect the flow status of existing liquid.
2. Is there any way to change the size of the block when you use a block cursor?
It appears not. It fills the entire 16x16 map block that the cursor is in. It would be really cool to do it to the currently selected designation rectangle, but it looks like dfhack doesn't support that.
3. After you place some static liquid, how do you get it flowing again?
At a guess, position the cursor and use "dfliquids f f+ block". Or "dfliquids f f+ point" to do one tile at a time.
4. What exactly does the 'don't change flow state (read state in flow mode)' function mean? Also, whats flow mode?
It seems to mean that the "f." option prints the value of both flow flags (flow bits) for each tile in the 16x16 map block the cursor is in, instead of forcing those flags to be true (flowing liquid) or false (standing liquid).
"flow mode" controls whether all the liquid on the map block under the cursor gets set to flowing liquid or standing liquid or unchanged from its current state. The default is "f+" making it flowing liquid, which is probably what you always want.
5. The readme on the DFHack thread said that I can remove liquids using the DFLiquid tool, how do I do that? Besides turning it into obsidian.
Maybe by setting liquid amount to 0. Try "dfliquids w 0 block".
Incidentally, you might experiment with the undocumented command line options "column", "starruby", and "darkhide". Of course they might break your game, they must be undocumented for a reason.