I wanted to provide a follow up on how this went. I uploaded the latest (v3) Websense iApp to the LTM. When I went to install it, I got an error message saying (I'm paraphrasing) that the object already existed. When installing, there is a check box to overwrite the existing config. So, I checked than and re-tried the install. That worked.
Actually, it worked brilliantly: All of the existing iapp settings were retained and the problems of the old iapp version were fixed. As far as I could tell, there was no downtime (of course this virtual server handles web browsing traffic, so it's all transient anyhow)
Our LTM-Websense integration has been problematic from the start. It's a seemingly simple process, but the bugs in the old iapp version were a huge problem that clouded the original deployment of things. It's good we're finally getting some positive movement.
The remaining big unknown here is how much load our LTM will see when we have 500 megabits of web browsing traffic running through it. The LTM interfaces in question are 1 GB (LACP pair) so I am not worried about them. I am more worried about the 4200v CPU utilization. We are phasing in a few IP subnets at a time, so we can monitor the load over time and see how the LTM handles it.