No. If you mess around with your 2018 return you will change it, make a mess of it, and be unable to transfer it to start your 2019 tax return.
And you cannot start a new "dummy" online account right now, since online tax preparation is closed until the 2019 software is released in late November/early December.
You can try the tax caster tool:
https://turbotax.intuit.com/tax-tools/calculators/taxcaster/
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
