This regulation specifies the security structure of a web site for Citizens' Initiatives.
I think that such a system should allow citizens to change their vote in subsequent sessions yet this regulation demands that data should not be alterable. However, such a limitation can be worked around by having the facility for later dated votes to supersede earlier ones.
The ability to change your vote allows voters to cast a vote at a time which is convenient to them and then change it later if they change their mind. It will reduce the information load on the system as a ballot reaches its deadline, will likely increase voting numbers as it makes the system more convenient and facilitates an increasing amount of debate, closer to the deadline, to have the chance to change the outcome.