How to make something spawn at a point from replicated storage?

You could do something like:

local RS = game:GetService("ReplicatedStorage")
local crops = RS:WaitForChild("Crops") --folder of crop stages

function newgrowthstage(originalobj, stagenm)
	--gets new crop with the name of whatever stagenm is
	local newcrop = crops:WaitForChild(stagenm):Clone()
	newcrop.Parent = workspace
	
	--sets cframe to the previous stage's cframe, where the previous stage is originalobj
	newcrop.CFrame = originalobj.CFrame
	
	--destroys the previous stage
	originalobj:Destroy()
end

Though you'll have to keep track of the objects somehow, perhaps an array that keeps track of both the actual model/part and what stage it is currently at.