There are currently three relevant ways to customise or extend SAP Business One. Firstly, there are the SAP board tools: the Software Development Kit (SDK) and the built-in functions such as user-defined objects, tables and fields. This also includes SAP's UI designer.
Based on the SAP SDK, it is also possible to operate with frameworks from SAP partners, such as the one from coresystems (coresuite country package). The same applies to the usability package (b1up) from Boyum.
The latter two frameworks have become very powerful over the years. The adaptations and extensions of SAP Business One are thus considerably accelerated. However, one can say that nothing that is possible with these tools cannot theoretically be implemented with the SDK. Secondly, of course, everything that is adapted to a standard software should always be considered carefully. The rule here is always: first check how a requirement can be implemented in the standard. Because sometimes you solve a problem at one point, but raise a new problem at another point in the process.
Sometimes adaptation tools also blur the line between Customizing and coding. They also have the possibility to include their own code.
In a webinar by Boyum, we demonstrate relatively well what is possible, for example, with the 'Advanced Item Placement Tool' and how the SAP standard UI designer relates to it.
It is noticeable that Boyum has already gone the extra mile here. However, it is also good that Boyum describes what one has to bear in mind with partly massive interventions and where the limits lie.
However, if you follow the rules on Customization of SAP Business One, one thing can be guaranteed: Unlike some other ERP packages with customisation options, the release and update capability of SAP Business One remains unaffected.