Hi jhuffa,
There are a couple ways to do this.
Click the table cloth in this example code snippet. At the lower left, you can click the "View Code" button.

Here is the API documentation for the function used.

You can also accomplish this with logic nodes. In this case you are changing out the material not the texture. So you would be changing the materiel for all or part of your T- shirt. Inherit Material Node.

I am not sure what you are asking. You need to have the "Force Dynamic Object" checked if you are going to perform certain operations.

API methods that concern object movement, copying and animation (both object and node material) can only be applied to dynamic objects. In order to make the movement of the object without dynamic settings possible, it is necessary to activate Force Dynamic Object option in its settings.

Link

Demo Page

I don't have much experience with instanced particle systems but I suspect the particle objects are not treated as normal objects by the engine.
I am wondering if your objects was instanced using the instancing API, it might work with the pick_object() function.

Are you getting any errors in your browser console console?

Outstanding!

I am working a project now with an env texture that is 16385 X 8110 using Cycles nodes. It runs fine but my GPU is an Nvidia GTX 980. I may tray to cut it down a bit but this project is designed to take advantage of high powered PCs.

I am pretty sure I noticed the Everest project loading in tiles dynamically. You could end up with much higher resolution that way but you also have to deal with looking at blurry tiles for a second while it loads in the high res tile.

So your answer depends entirely on your target audience. Gaming rigs can handle some huge textures but if you want it to work on mobile device, it needs to be smaller.
You also have the option of Resource Conversion in your Project Manager. It will automatically make smaller texture sizes that will load on less capable devices. There are some URL parameters that will allow web player project to load compressed textures. Attributes.

Here, you can see the results of my conversion. The min50 is the scaled down version.

I was doing a project with tons of logic nodes and I thought of a new type of node that would allow you to make reusable node groups (like functions). You already have Entry Point nodes that can be set to run from a script. If you made a new node called "Run Entry Point" with a parameter for one of the entry point nodes, you could make reusable node groups that would not run until called. For example you could make a node group that made various objects get hidden or shown based on some variables. Once the variables changed, you could call the node group and it would process all the show/hide nodes according to the new variable values.

Hi ptab.
Yes, it can be done but you need a local server of some kind. Yuri wrote a good post on this with a few useful links.
You can read it here.

That is awesome to have some of your work built into Blender now!