you already can, While cosmic stuff is on the AUR i've been having issues with it so I use my own scripts I have here https://github.com/Quackdoc/pkgbuild-scripts/tree/Master/cosmic-epoch

you can add the repo as a paru repo if you have it;

[quackpkg]
Url = https://github.com/Quackdoc/pkgbuild-scripts.git
#Path = /home/quack/code/pkgbuild-scripts
Depth = 4

then install it using paru -S --rebuild cosmic-applibrary-git cosmic-bg-git cosmic-comp-git cosmic-edit-git cosmic-files-git cosmic-greeter-git cosmic-icons-git cosmic-launcher-git cosmic-notifications-git cosmic-osd-git cosmic-panel-git cosmic-randr-git cosmic-screenshot-git cosmic-session-git cosmic-settings-daemon-git cosmic-settings-git cosmic-store-git cosmic-term-git cosmic-workspaces-epoch-git xdg-desktop-portal-cosmic-git

you will also need cosmic-applets-git I need to patch mine to disable LTO=fat with LTO=thin in cargo toml so it's not part of the above command. Note I haven't done a clean build on these, but they should mostly work. if you run into any issues lemme know and I can try and fix them.

cosmic-greeter can be enabled with cosmic-greeter.service I think you need to manually install greetd im not sure I have added it to deps. using cosmic-greeter isn't necessary however.

EDIT: it is somewhat likely that I may have messed something up, but as it stands i'm currently actively using cosmic comp right now