You can create and modify cell links by using any API operation that creates or updates cell data. Creating or updating cell links via the cell.linkInFromCell attribute is a special operation. A given row or cell update operation may contain only link updates, or no link updates. Attempting to mix row/cell updates with cell link updates will result in error code 1115.
When creating a cell link, cell.value must be null (the data will be pulled from the linked cell).
A cell may not contain both a hyperlink and a cell link, so hyperlink and linkInFromCell may never both be non-null at the same time.
A cell link can only be added to an existing cell, so the cell.linkInFromCell attribute is not allowed when POSTing a new row to a sheet.