So, I've been flying around in a Private server, and I noticed there are some holograms, that are.. unusual. Like I know you can make Hologram solid with [name]:1, but how do you make your Hologram giant? What are other settings/options of customising a hologram?

Giant holograms are caused by the blockdata tag {scale:<number goes here (remove the brackets too)>}, for example {scale:10}.

Another tag is {small_arms:<0 or 1>}, which switches it between Steve and Alex models respectively.

A third useful tag is {username:"<name>"}, which acts exactly like it would in an anvil renaming, but you need quotation marks around it.

Is it possible to change blockdata tags in a DMU public/private server and how?

Only staff can