Hi,
Yes, it's gonna have positive effect, increasing the BW you're shaping to, as this is what you want. There is no bad impact with doing the change live, however if this is a critical device, do it in a maintenance window, as nasty bugs could show up. For example, i was "able" to completely make a VSS system reboot itself, by just configuring an "interface description", and i have more such stories :)
Regards,
Cristian Matei.