Assuming that you have the permission to do so then there should be no reason why you could not. The following example assumes that you are using Windows Authentication:
sqlcmd -E -S computer\instance -d database
alter procedure testtable_pricesmaller
@pricelimit money
as
select * from testtable where price = @pricelimit;
go
Alternatively if you have an existing script file that has the command you want to run you could use the -i option to run that file:
sqlcmd -E -S computer\instance -d database -i file.sql
Here is some more information on the sqlcmd utility that you should find helpful:
http://msdn.microsoft.com/en-us/library/ms180944.aspx
I hope this helps you.