Q: 

Can I downgrade to an older EIVA software version, e.g. from NaviModel Pro 4.8 to 4.6?

A: 

We do not support downgrades (NaviModel 4.8 to 4.6) when installing NaviModel into the same folder, only upgrades (NaviModel 4.6 to 4.8).

Downgrades might result in dependency issues, e.g. NaviModel error: Could not load type 'Eiva.GDAL Initialize' from assembly 'Eiva.GDAL, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'. 

If you need to downgrade, uninstall NaviModel 4.8 before installing NaviModel 4.6.