Is it allowed to edit IFC?

Yes, of course. You cannot use data if you are not allowed to touch it, can you? Think about it. What is the first thing you do in Excel when you start working with the data? You rearrange columns, you may rename them. You correct the values or fill in the empty ones. You add a new column to enrich your data with calculations. Then you create a graph and use the data. How do you work with structural drawings? You enrich, measure quantities, you classify the data while extracting it for your purpose.

What Simplebim does to IFC data is no different. It is just that IFC is a much more complex data structure than a simple table in Excel. And Simplebim does much more advanced things to the BIM model data than just adding columns.

Why cannot the designers put all the data into their models? In fact, some of the software vendors claim in their communication, that only the designers should be allowed to edit the models.

Well, yes only the designers should edit the data that they create themselves. But. This is a very narrow view to BIM usage. The design models are only the beginning of the BIM lifecycle. Other parties downstream take the design models as input and enrich them further with the data they create.

Maybe the better word to use here is manage or process, instead of edit. The basic data management rule here is simple: everybody should edit/process/manage and enrich their own data. The data they create or produce, with the tools they have. The designers create and edit their data in model author tools. The production teams create and edit the data they produce in their own tools.

The catch with IFC is, that it can and should contain both design data and downstream data. You need to be able manage this data, to enrich and re-structure the data in the IFC models, such that it becomes fit for your purposes. The alternative would be to demand IFC models that always fit your needs 100% from others, which is neither practical nor realistic by any stretch of the imagination.

All that said, Simplebim does not even edit your original IFC file. It imports and merges IFC files, processes them, and then exports the processed data back to IFC or to data tables. The original always file stays the same!