Climate change model
Both are relatively small secondary effects on global temperature, but at the same time, both are worth studying.

Ice acts like a heat sponge.   It takes heat to melt ice (that's kinda obvious) and less obvious, forming ice releases heat.   Large blocks of ice cool the air when it's above freezing and warm the air when it's below.   Even as ice changes from solid to liquid, without changing it's temperature, the energy change is significant.   This is called it's latent heat of fusion or LHF.

By this article about 2% of the trapped heat goes into melting ice.   A 2% variation on heat that would otherwise, warm the air or oceans or escape into space is almost small enough to ignore, but the effect grows much larger locally near glaciers (perhaps as high as 25%, but the source I found for that isn't one I'd call credible), but certainly, the effect is significantly higher than 2% in the arctic and antarctic.

Latent heat of fusion is also important in calculations for the total energy balance and here's an article from IPCC AR4 that discusses LHF.  

As pointed out in the comments, melting sea ice also changes ocean albedo and can lead to a rather quick change in absorbed heat and a reduction in the light reflected back into space.  This also happens on land, mostly snow cover, (as glaciers melt too slowly for that kind of year to year effect), but I don't think that's what the question is asking.   



The 2nd part, the change in salinity is (to my knowledge, and I invite correction from anyone who studies this professionally), but from what I've read, it's much more complicated to model than LHF.   It's certainly something that researchers are aware of, both the warming arctic and changes in salinity might effect ocean currents.   Unlike air, where temperature drives density and that leads to low and high pressure and updrafts and basically, weather, oceans have two factors that can effect water density - temperature and salinity.   Warm water is lighter than cold water, but lower salinity water is also lighter than warmer, more salty water.

Small changes in salinity in ocean surface water doesn't have any real effect on temperature directly, but the effect on ocean currents is worth studying because changes in ocean currents can effect temperature significantly, certainly on a local scale, and globally too.

Modelling this, like modeling the rate of future glacial melt, may be close to impossible and when it's written about, it can sound more alarmist than science, so it's a subject that has 2 key problems, difficult to predict (even in the hard to predict climate change models the effect of salinity changes on ocean currents are especially tricky), and it's the kind of thing that might invite shouts from the other side, like Wiesław Masłowski's infamous study that suggested the arctic might be ice-free by 2013.   He was a graduate student, not a climate scientist and his was a good study and preliminary.  It should have been subject to peer review, instead, (in part because Al Gore used his study in a speech), it became a famous example to alarmism and was subject to much ridicule that persists to this day.

Scientists are certainly aware of the possible effects of salinity changes and the effect that might have on ocean currents, but it's very difficult to model and mostly written about observed effects in the present, and mostly not written regarding future forecasts.   Predictions like "the Atlantic current could shut down" may be based in science, but low probability predictions like that tend to invite criticism.

Fresh water/ice melt is discussed in Wikipedia here and here's an article where the opposite is happening.   As arctic sea ice recedes, the lighter, less salty water on top isn't present as much as it used to be and the arctic-ocean stratification is going away.   Article on that here.

It's also worth noting that glacier fed rivers will affect the ecosystem down-river, putting less or more water into the environment leading to less or more greening and less or more water evaporating off the river into the atmosphere.   It's more common for rivers to be fed by snow melt than glacial melt, but the glacial melt should be studied too.   Changes in greening down-river and in atmospheric water vapor also effect climate, so, as someone said in the comments, there are a lot of moving parts to the climate picture.   

Generally speaking, scientists are aware of all of this and as much as possible, study it and include it in models.