if some one change his signature back link and suppose forum is already linking back to particular site so can it will effect back link....
Much depends on how fast google reindexes the change. I find that often google has old copies of pages with old links, sometimes over a year old.
Right, It will be good for the new pointed link if the page is already re indexed. Otherwise, the flow will remain the previous links.
yes, if you have already some no.of posts with a signature link of one site, and suppose if you will be changing the signature link of another site, the entire signature of link all posts, including existing posts, will be changed with the new signature link.
I tried it and there is fantastic result produced as , although former site, towards whom the "changed signature" points out get benefit yet the later also not faced any degradation.
User name inside the site home page is DOFOLLOW, Google will think that is the reverse link, and will also get permission