FYI, in BPMs you can also use the following for your UD Fields.
ttABCCode.UDField<System.String>("MyNewColumn_c")
row.SetUDField<System.String>("Column", "Hello World!");
Example:
var partPlants = from tpp in ttPartPlant
where tpp.Updated() && tpp.UDField<System.Decimal>("Number01") == 0
select tpp;