State machine WF, persistence problem

Hello,

    Anyone has any ideas? suppose I do some state machine WF like
 
    1--> 2 --> 3, and keep data in persistence DB

    And i have to change some state machine flow, some old instance not complete yet( still in some state in flow ), like

    1--> 2 -->2.5 --> 3

    Do any problem with old instances? for example those instances in state 2

Rgs
Piyaret