Thanks for the links!
Indeed, I did regain the access from the blacklisted IP at the end of the day (probably after 1hr would be ok too). After all, the 850 char limit may be imposed for the first ever post only, may be also on the registration day (and when it falls on a Monday, in November etc. ...). With the first topic successfully posted (from another IP), the supposed limit does not seem to matter anymore. Oh, well...
However, learning about the Forum hosting saga made me want to join the community efforts in finding a more robust way to TCL Forum operations. Hope these efforts will get to fruition soon.