Cisco ASA VLANs and Sub-Interfaces

If I have an existing interface on an ASA5580 redundant pair and want to create subinterfaces on that interface are there any production challenges I will face? Let say I have Gi8/2 with an existing ip 172.21.16.254, now I want to create two subinterface on Gi8/2 one for 172.21.16.x and one for 10.248.80.x. I know how to create sub-interfaces however not sure of the impact, I know when I move 172.21.16 to a subinterface I will lose connectivity while I reconfig the interface but I am wondering if I need to reload the ASA once the config is done or will it update as I config without a reload requirement. Any other thoughts you might have. I also realize that I need to change the access switchport connection to a trunk port.