I once wrote scripts to do this.

At the moment I can only find the trim script:

select 'update ' + o.name + ' set ' + c.name + '=RTRIM(' + c.name + ')'

     from syscolumns c, sysobjects o

 where o.id=c.id

 and c.xtype=167

 and o.type='U'

order by o.name,c.name

This generates the script that does the real work. The alter table script can be generated in a similar way.