This information is taken from a thread about this on the SkyWest forums a few years ago answering this exact question.
"CF34-3A1 = Series 100
CF34-3B1 = Series 200
Add center fuel tank option = ER
Add center fuel tank and buy 53,000 lb MTOW placards= LR
So, SkyWest's original aircraft (i.e.403 SW) began their life at SkyWest as Series 100ER, but most are now “technically” Series 200LR” (upgrade engines to B and up MTOW to 53000lbs)."
"The actual "aircraft model" is a CL600-2B19 Series 100. That defines the up to 50 passenger CRJ. That is the only "legal" description. If you look on all CRJ FAA Airworthiness Certificates they will state "Model CL600-2B19 Series 100".
When marketing becomes involved we now have four variants that mostly differentiate between engine type and MTOW.
Series 100ER CF34-3A1 51000 MTOW
Series 100LR CF34-3A1 53000 MTOW
Series 200ER CF34-3B1 51000 MTOW
Series 200LR CF34-3B1 53000 MTOW
Since the Series 200 is essentially a "marketing" variant, there is no method to "convert" a Series 100 to a Series 200. Transport Canada (certifying authority) makes reference to Model CL600-2B19 when it issues documents (like ADs) on the Regional Jet.
Both engine types are listed on the Type Certificate Data Sheet and AFM and the 53,000 lb MTOW is an "option". Specific AFM data exists for all configurations. Another way of looking at this is the Series 100 airplanes had CF34-3A1 engines installed during production and the Series 200 airplanes had CF34-3B1 engines installed during production.
There are other "marketing variants" like the Series 240 and 440 (40 and 44 seats respectively) but lets not go there and get even more confused!
The CRJ 700 is a CL600-2C10.
Are we confused yet! "
What shows up on the ATC paper strip is CRJ2 for all SkyWest airplanes.