When transcribing according to the “Provisional Guidance for Transcription Using the Nemeth Code within UEB Contexts” or the upcoming “Guidance for Transcription Using the Nemeth Code within UEB Context," tactile graphics can be dealt with on a case-by-case basis.
If a graphic occurs between two items that must be in Nemeth Code, then Nemeth Code should almost always be left in effect for the graphic.
If a graphic is not flanked by material that must be in Nemeth Code, then the transcriber has to determine whether Nemeth must be used for that specific graphic.
If a graphic is not flanked by material that must be in Nemeth Code, and nothing in the graphic would need to be in Nemeth mode in the text, then I would not use Nemeth anywhere in that graphic.
Alternatively, all graphics can be transcribed in Nemeth mode. In this case, a TN at the beginning of the volume should alert the reader to this arrangment, which is most useful when all or nearly all graphics in a transcription require Nemeth to be used.
If that does not fully address your question, or if you have follow-up concerns, please do not hesitate to post again.