Players can create clones of, for example, tools from a place such as server storage using the :Clone() function.
local Tool = game.ServerStorage.Tool:Clone()
but before they can Parent the tool into workspace, can the player manipulate said item before it can reach the workspace? For example:
local Tool = game.ServerStorage.Tool:Clone()
local Part = Instance.new("Part", Tool")
Part.Size = Vector3.new(1,1,1)
Tool.Parent = workspace
if this is possible, are there problems that could occur and anything I should know before doing stuff like this?

3 comments
Don't use the 2nd argument of Instance.new
So i just set it to Part.Parent = Tool? I could still manipulate it before it reaches workspace right?
Clients cannot access ServerStorage, so the answer is no they can't. Until you parent it into workspace, they won't be able to even see it.