Well, you'd have to create the GUI front end yourself, but to extract the current description from a field call the following (let the column name be NULL to get the table description):
SELECT @OldDesc = CAST(D.Value AS nvarchar(128))
FROM ::fn_ListExtendedProperty('MS_Description', 'schema', 'dbo', 'table', @TableName, N'column', @ColName) D;
In order to update a description, you first have to remove the original one (if it exists), then replace it with a new one:
IF NOT (@OldDesc IS NULL OR @@RowCount = 0)
EXEC sp_dropextendedproperty N'MS_Description', N'schema', N'dbo', N'table', @TableName, N'column', @ColName;
EXEC sp_addextendedproperty N'MS_Description', @NewDesc, N'schema', N'dbo', N'table', @TableName, N'column', @ColName;
I hope this points you in the right direction.
--Aaron