JD_Wolfe

Repotting at this time shouldn't be problematic for you and it's a good idea to get it out of that loamy/clay soil it's in. That said, the yellowing of some of the leaves could be unrelated to the soil. Are the leaves themselves browning or are they yellow with little flecks of green that seems to be leeching out of them? If they're brown then it's probably the soil. If they're yellow with remnants of the green chlorophyl draining away it could be indicative of chlorosis which can be caused by a couple of things. I know for my elms the leaves yellowed from Black Spot fungus. Avoiding the new spring leaves when you water will help avoid Black Spot (you can usually tell it's Black Spot, because, like the name implies, the leaves have little black, mottled spots). Try repotting first and avoid water on the new growth until it's had some time to harden off. If you're still getting yellowing leaves after a month or so, you might want to consider fungicide drench (Daconil is supposed to be good -- can't get it here unfortunately).

Best of luck,

Jeremy