Yep, it's easy but there are a couple of things that the doner bike needs. If it is a front wheel kit it must be a steel fork as all the drive is transmitted through the dropout and likewise a rear wheel kit needs a steel frame but OLN size can be an issue.
There must also be somewhere to mount the chosen battery, there are 'seatpost' mount batteries but these are pitifully small capacity.
We have 2 conversions, Maz's Dawes Geneva and my Trike which have both been trouble free for nearly 4yrs and 3yrs respectively, both are Cyclotricity front wheel kits with rackmount batteries.