OP wrote:
"The conversion seems simple enough, but my concern is about breaking the screen even if the proper tools are used to open it. Is that a serious risk?"
Yes, it most certainly
IS risky.
There are numerous reports from folks who "thought they could do the job", opened it up, and then...
broke something inside.
There's a better way:
Get a USB3 external SSD of sufficient capacity.
Just plug it into a USB port and use it that way.
You can even make it into an "external booter" if you wish. The iMac will run great that way.
Booting and running this way (or just using the drive as "storage") will give you 85% of the speed (or a little more) than you'd get by having the drive installed inside.
Yes, it's a bit slower (but not much).
The upside is you DON'T break anything by opening up the iMac.
Take care:
If you buy a "bare" SSD and an external enclosure, MAKE SURE the enclosure you buy is SPECIFICALLY STATED to support UASP.
Or… buy a "ready to go" SSD like this:
http://www.amazon.com/exec/obidos/ASIN/B00ZTRY532?tag=delt-20