Here is a hacked together way to update the hole depth manually. This isn't the ideal way, but it seems to work for me. I am not sure what the rest of your code looks like, so you may have to tweak the beginning where you are getting the hole object. Instead of searching for the hole feature by name like you used to, for this to work you have to find the hole feature object in the part. If you want to post the rest of your code I could hopefully help you fit this into it.
Also, note that I had to hard code the path to the thread.xls file. I am using Inventor 2020 so you may have to change that.
' Get active part. Assume a part is opened.
Dim part As PartDocument = ThisApplication.ActiveDocument
' Get first hole feature in the active part.
Dim hole As HoleFeature = part.ComponentDefinition.Features.HoleFeatures(1)
' The thread designation to change the hole to.
' *******CHANGE THIS LINE *******
Dim newThreadDesignation As String = "M6x1"
' The thread class to change the hole to.
' *******CHANGE THIS LINE *******
Dim newThreadClass As String = "6H"
' The path to the thread.xls spreadsheet.
' Change to match your setup.
' *******CHANGE THIS LINE *******
Dim spreadSheetFilePath As String = "C:\Users\Public\Documents\Autodesk\Inventor 2020\Design Data\XLS\en-US\thread.xls"
' The sheet name in the thread.xls spreadsheet for the
' thread standard you want.
' *******CHANGE THIS LINE *******
Dim spreadSheetSheetName As String = "ISO Metric profile"
' Change the hole to the new thread; except the depth.
Feature.SetThread(hole.Name, spreadSheetSheetName, newThreadDesignation, newThreadClass)
' Get the correct thread depth from the thread.xls spreadsheet.
' The column titles are on row 3 for "Thread Designation" and "Class"
GoExcel.TitleRow = 3
' Get the row that matches the new thread values.
' ie. the row with M5x0.8 6H.
Dim row As Integer = GoExcel.FindRow(spreadSheetFilePath, spreadSheetSheetName, "Thread Designation", "=", newThreadDesignation, "Class", "=", newThreadClass)
' Get the thread depth value at that row. Thread Depth column is column V.
Dim spreadSheetThreadDepth As String = GoExcel.CellValue("V" & row)
' Convert the thread depth from the thread.xls spreadsheet to a number.
Dim spreadSheetThreadDepthDouble As Double
Double.TryParse(spreadSheetThreadDepth, spreadSheetThreadDepthDouble)
' Update the hole thread depth in the model.
' The depth is in mm in the spreadsheet.
' Inventor uses cm internally; so divide by 10.
hole.TapInfo.ThreadDepth.Value = (spreadSheetThreadDepthDouble / 10)