We need advice on the best way to make adjustments to tens-of-thousands of assets at a time.

We are being acquired and need to adjust the cost, in service date, and remaining life based on the acquisition date.  We are looking at API's but don't know which ones to use or how to use them.  Also found a document about using Web ADI Spreadsheets but have the same problems (how to set one up, what API to reference etc.)  We can't be the first ones to have to do something like this.  Any advice would be helpful.