Questions about TFTP & function "Run As"

Hello everyone!
I have some questions:
1) Can I transfer more than 999 MB via TFTP? In Option -> Setup -> TFTP Server, I can only enter the 0-999 MB range. Manual editing of the configuration file did not give any result. TFTP protocol supports up to 4GB. And in other programs it works.
2) Can I launch actions using "Run As ..."? I need to run "current configuration backup" with one administrator account and use "cli send commands" with another account. Is it possible? This is due to the company's security policy... Or will I have to add 200 devices for each of the tasks?