So, it is very simple. We are allowed to pay more PP than we should and the number for PP will change into a negative value but here's the catch, we are allowed to have negative PP once per week and have to "pay" the "debt" before we can buy more. It's just like using our credit card.
Could you explain why you want this? Because to me it just doesn’t sound very handy to be in negative PP when you can just post more before you make a bigger purchase.
And wouldn't it be like that every user is instantly able to purchase the Vip-Rank? I see some holes here...
I really don't see a purpose for this, it would just make it too easy for people to get the VIP rank if they can just be charged into negative, if people want something they should just post and save up. Also keep in mind it may not even be possible to go into negative at all since we don't know how the currency system is set up.
It's an interesting idea, I like the concept but in execution it might not work. I'm not sure the system would allow it sadly.