The last company to offer the transfer from common to preffered was Hisu. The stock was way under priced and was merged with another company. They stated that the conversion was 1-100 and after six months you have the option of converting back with the pps at a new level.
Well, most did not and a 1-10000 took place and all common shares were reduce leaving investors who did not convert with nothing. Those that did convert were safe, but the pps would drop from 1 to maybe .01 in the next six months if not sooner.