Enable force merging of sessions of differing modalities

Feel free to disregard, but I keep running into this problem and it would be great to have a way to work around it easily.

We have a PET-MR scanner and have decided to keep to the combined PET-MR session datatype as it will simplify some of our processing pipelines. However, since PET-MR sessions can be very long (> 1.5 hours) and our radiographers tend to send the scans in batches. This means that even though I have set a long wait time before building sessions (30 min), sessions can sometimes be split in two.

For single modality sessions this would be okay as I could just merge the split sessions together. However, often the second batch of scans doesn't contain either any PET or any MR and so it gets identified as being a MR-only or PET-only session and then there is no way to merge it with a MR-PET session as the modalities differ.

So I was wondering whether there could a be a force checkbox that would allow merging sessions of different modalities for situations such as this.