Is it ok to replace a tantalium decoupling capacitor with ceramic?
It should be fine.
The choice of decoupling capacitors is one of those matters that can either solved with &quot;slap 0.1µF on that&quot; or weeks of analysis.
what you want is a big reserve of charges to allow your chip to pull current without dropping the supply voltage, and a small but low ESR (equivalent serie resistance) cap to shunt the high frequencies that could come from it.
As a rule of thumb, 1µF + 0.1µF, both in ceramic, should be fine for the most common applications, including yours. I recommend reading up on the subject, it has helped me drastically as a designer. This answer and this application note are good starting points.