You can do the work now, but just a word of caution. Dwarf Alberta Spruce is very difficult material to work with. Do a search here on it and read up.
It's not that it's weak or not hardy. It's the opposite. It's pretty impossible to kill one.
Its biggest problem is its upward-shooting branches. Ninety percent of the branches on your tree will have angles from the trunk that will make them very hard to tame into more lateral positions. to get the branches to set in "pine style" planes requires undercutting the branch at the trunk, wiring in place and hoping the branch doesn't die off.Over a few years, the callusing on the branch cuts "sets" the branch in place. Trying to only use wire on them results in ridiculous-looking "rainbow" branches with no character.
Trunk chops are ineffective if you're planning to grow it out for trunk taper. It will take decades to regrow a new, believable leader. Most people using these kinds of long bushy nursery grown alberta spruces jin the tops out of them to make them look like old tall, forest trees. You will never get noticeable even taper with a trunk chop unless you plant it the ground and do repeated chops there for 10-15 years...
That said, you can probably chop to your heart's content on this tree now. See what you can do with it. Experiment with pulling branches into lateral positions, deadwood features, etc.
