changing shoulder width...

[...]

Well, in the interim even fat mass requires bigger clothes as well, until it's gone. I've gained about 15 pounds, not all lean mass, and noticed that my shirtsleeves are riding up my arms like some adolescent who has outgrown his go-to-meetin' clothes.

I gain all over so my necksize is up a full size as well. Waist is actually down.

The problem with answering this question with specifics is that everyone's pattern of growth and bulk-cut is bound to be different. Ten pounds of muscle will be different on different folks.

If your shoulders build easily, prepare to need longer sleeves in time.

I'm facing the same issues and can't wear shirts I wore two months ago. MJL's point would be that quick changes will only be an issue for about six months, when changes will come more slowly.

My plan is to buy new clothes if I must, when I must. (Can't state the obvious much more simply than that.) Write it off as part of the price of improvement.

'Improvement' = Bigger Muscles (Wow. That's deep.)

Maybe not 'stylish', but certainly 'most readily available'. I find it rather amusing and kinda sad that as an official fatass (on the McDonald Obesity Scale) I wear dress shirts labeled 'Athletic Fit'.

: lbs of mostly lean mass.

Define 'do things right,' if you don't mind. I'm a newbie and if I could gain 10lbs of muscle in 6 months I'd shit a brick.

Well, there go the 10 lbs.
http://www.stumptuous.com/weights.html

It's all about relativity - if you decrease your wast 1 inch then you have effectively increased your shoulders one inch.

Also, only a small increase in shoulder width is quite noticable.