Can I convert from a 52/42/30 crankset to 50/39/30? I need to update my 9 speed triple crankset at 52/42/30, and those combinations seem difficult to find when I'm also looking to upgrade. A more common teeth combination seems to be 50/39/30, but I'm wondering what else I might have to upgrade if I make this move? Or is there another combination that I'm not aware of so that I don't have to make these updates?

Specifically:


Do I need a new front derailleur? (currently have Shimano Tiagra T, down pull, braze-on type w/34.9 mm clamp attachment)
And I have a 9 speed SRAM chain and 9 speed SRAM cassette. Will those need to be updated? 
Lastly I have 9 speed Shimano Tiagra STI Dual Controls, will those need to be updated as well?


Any advice would be great. Thanks!
When you do drive train swaps, you need to check the chain length, and the capacities and limits stated on the front and rear derailleur (look at their data sheets). 

1) Check the data sheet for your front derailleur. It will specify the sizes of the chainrings and the teeth differences required. Almost surely it will be fine though. You'll have to fidget with the clamp position a bit. 

2) You'll end up shortening the chain by a few links, ideally (you can run a too long chain safely, but why bother?). The cassette doesn't need to change. 

3) No - so long as you stay with a &lt;=9 speed Shimano RD and Shimano Road FD (I believe &lt;=10 speed), you're OK. The RD doesn't need to change either. 

Aside: 52/42/30 cranksets aren't uncommon.