Assign 2D frequencies to (existing) 1D frequencies or set them manually

If a 1D (e.g. 1H) is already picked, or if a 13C frequency is pre-defined (e.g. from a picked HSQC) when picking an HMBC, there should be a possibility to define, that one of the signals has to share the same shift as the already existing one (or vice versa). Or, at least, as for the 1D it is possible to manually define a frequency, one should be able to define/edit by hand the frequencies in both dimensions