Currently undergoing IPL hair removal. Can I then switch to a YAG laser for yearly maintenance?

IPL is used for lighter skin and isn't the first choice for Laser Hair removal.  There are newer and better choice for Laser Hair removal.  Lighter skin an Alexandrite Laser is usually best, for darker skin a Yag is best. 

Thanks for your question.  It sounds like you are not going to a facility with up to date equipment.  If you bikini line is too dark, you are probably border line any place else and at risk of being burned.  I would make an appointment with their supervising physician to get your money back for unused sessions.  If they can't treat you safely, they shouldn't treat you.Based on your skin type,, you should have sought out a laser vs. IPL to help avoid complications.  Almost all newer lasers are safe for all skin types and have features built in (such as sapphire cooling tips) to make them more comfortable.  Some of the newer technology is also more efficient, allowing for lower energy settings to be used with better results and less discomfort.  With modern equipment, your treatment should only be mildly uncomfortable, but not painful.  We never use numbing cream for LHR.  We want our patients to be able to tell us if they feel pain or an unusual level of discomfort.We recommend finding an experienced and reputable provider in your area with updated equipment.  A consistent overlapping technique is the key to avoiding patchiness in LHR.   Calibration and power of the laser is important for a safe, comfortable and effective treatment.  Find out what laser they will use and if it is under a maintenance contract.  If their laser isn’t calibrated on a regular basis or is underpowered, your treatment may be painful or inefficient. After a series of 6-8 initial treatments, you may need a touch up every 3-5 years.

The short answer is yes.
IPL works great when you have light skin and dark hair. If the skin is dark, you'll need an ND-Yag laser.