Basically when the piece of timber is directly above the rigging point and is then inverted 180 degrees and lowered down I call it blocking down or dynamic blocking.
This is one of the bigger lumps we did, the rope should have been allowed to run a lot more to minimise the shock load, but we were a bit over cautious and put one too many wraps on the lowering bollard, which in turn led to too much friction on the bollard and the shock load on the system you see here.
As a side note if the stem is to be dismantled in sections but not rigged, I call it chogging down. Don't ask me why, just always have. The guys on the ground always seem to know what I'm on about anyway.